Reginald Kastle

Reginald Kastle, known as Ryoga Kamishiro (, Kamishiro Ryōga) in the manga and Japanese version and nicknamed "Shark" (シャーク, Shāku) in all versions, is one of the main characters in Yu-Gi-Oh! ZEXAL. He is one of Yuma Tsukumo's close friends and rivals. He was originally an arrogant and callous person, but has grown quite humble. He is later revealed to be Nash (Nasch (ナッシュ, Nasshu) in the Japanese version), the leader of the Seven Barian Emperors. Determined to not let tragedies befall his people again, he betrayed Yuma and his friends to safeguard the Barian World. He is the only Barian Emperor not to be absorbed by Don Thousand, as well as being the only Barian whose original memories were not altered. He later vanished after losing to Yuma in a Duel that had the Human, Astral and Barian Worlds at stake. He along with the Seven Barian Emperors were revived by the Numeron Code.

Appearance
Shark has dark blue eyes, pale skin and dark purple hair, which resembles tentacles hanging down, referencing his Deck theme of aquatic creatures. These "tentacles" slightly resemble pigtails, but curl up on the end. He also has a light blue "crown" in front of his forehead. His accessories include a grey, shark tooth-shaped locket, which contains a family photo of his parents, as well as himself and his sister Rio Kastle as children. He also has a scar on his right shoulder. He also wears two grey rings on his right hand, but he later gives one to Rio. He also owns a grey and green Duel Gazer with a red lens and a yellow spike as well as a blue D-Pad. Upon regaining his Barian identity as Nash, he threw away the locket and replaced it with his own Barian Emblem pendant, though he regained the locket after his revival. His attire includes a dark purple jacket over a maroon shirt and dark blue pants with white, green-gems shoes. When in his school attire, he wears a white shirt with green-lined sleeves, tie and a collar. During his National Duel Circuit days, Reginald wore a white top with a purple waist coat and his usual dark pants.

As a Barian, he has a magenta skin tone and red and blue heterochromatic eyes with aqua markings on his face. He wears a crimson cape and copper-colored guards on the wrists, shoulders, and his legs are tipped with red stones and also wears a 'H'-shaped belt. The Barian Emblem pendant becomes larger and is engraved onto his chest. His tentacle-like hair gains more volume and he also wears a copper-colored crown piece with a red jewel on his forehead.

During his past life, Nash wore golden armor over a mesh shirt, gauze on his left arm, a light brown shirt, silver pants, a blue cape, and the original Barian Emblem on his chest in the form of a pendant.

Personality
Shark can be classified as a typical loner, being indifferent and cool about most things, usually sporting a stoic face or scowl. He prefers to be alone and doesn't follow a crowd, as his encounters with Yuma and others are often brief before he walks off. He also has displayed little interest in school, having had stopped going to Heartland Academy after his loss to Yuma. He still skipped class regardless when he decided to come back and would idly spend his time on the school's roof, but is said to be good at studying. Despite Shark's aloof and cold nature, many students at school respect his Dueling skills and he's secretly popular with female students, however Rio mentions that he is still disliked and feared by other students. Shark is shown to have a soft side, but has only shown it to two people - his sister and Yuma. Regardless of this, he can be insensitive and callous to both, causing fighting and arguing between them.

After being disqualified from the National Duel Circuit, Shark became bitter and uncaring, the way he held himself at the beginning of the series. Cold and malicious, Shark flaunts his power by taking the Decks of the people he defeats, making them squirm in the process, such as when he defeated Bronk Stone. When he becomes possessed by the "Numbers", he becomes quite violent, destroying the scenery surrounding him throughout his first Duel against Yuma, and also defeating several Duelists brutally when he was briefly possessed by "Number 32: Shark Drake.

However, he does have some honor, as he returned Bronk's Deck upon losing to Yuma as he promised and keeping all the Decks he'd stolen from people completely intact. His first defeat to Yuma has humbled him in a way that he is no longer overly cruel to people, as shown when he returns Yuma's pendant after winning an Ante Duel with it at stake. He also seems to put more faith in bonds and friendship, shown by his willingness to form a team with Yuma during the Tag Duel with Scorch and Chills. He further entrusts Yuma with a card that would allow them to win the Duel. Shark also tries to rescue Emperor's Key from Kite Tenjo and Orbital 7 when it is stolen, clearly stating that he sees Yuma as his friend. In the Duel with Kite, Shark remembers Yuma, and that Yuma would never give up.

Shark's friendship with Yuma also helped him in handling the "Numbers" cards. When "Number 17: Leviathan Dragon" came in contact with him, it easily took hold of him. However, he was able to fight off the influence of "Number 32: Shark Drake" because of his bond with Yuma, making him the first known person to be able to resist the influence of the "Numbers" without a special item or power. Despite being able to initially resist the influence, Vetrix said that it did infect him and it will amplify his darkness caused by his desire to take revenge against Quattro. However, after a Duel with Yuma, and seeing his bumbling antics, the darkness had disappeared.

However, after accepting his fate as a Barian, he adopted his cold personality again, saying that fate drew him and Yuma together to fight against one another. Unable to consider peace as an option despite his friendships with Astral and Yuma, he attacked Earth with the other Barian Emperors. He is shown to act ruthless when Dueling, as shown during his Duel with Quattro. Throwing himself fully into his Barian persona, he incited his opponent's anger, wanting to be hated and aiming to make both himself and Quattro forget about his time as "Reginald". However, it was shown he was doing this to protect the people of the Barian World. Also when Girag appeared to be in danger, Nash immediately attempted to rescue him, showing he cares for many, if not all of the Barian Emperors (with the obvious exception of Vector). He even burst into tears at witnessing Dumon's death. He also expresses sadness at Mizar's death.

In his final duel against Yuma and Astral, Nash was shown to be grief-stricken for having failed to protect the Barian Emperors and having failed to make their dream come true. He reaffirms his vow to save the Barian World with their spirits at his side and became increasingly more desperate to defeat Yuma and Astral as they continued to survive his every assault, culminating in him adopting a crazed expression in their final exchange. He was also visibly distraught when they finally managed to destroy "CXyz Barian Hope". Nonetheless, he returned back to his friendly self after losing to Yuma and being revived by the Numeron Code.

Abilities
After the Duel against Vector, Shark gained the ability to see Astral. Shark also merges his soul with his "Number", gaining the ability to perform Chaos Xyz Evolution with "Number 32: Shark Drake", acquiring a purple aura while doing so. He is also able to resist the "Numbers" influence after repeated exposure, no longer feeling the effects even from a "Chaos Number".

Shark has also demonstrated a few unique abilities: like his sister, he could generate a red aura around his body. The power of this aura fixed Dumon's Baria Lapris and allowed him to regain his Barian form. After recovering his Barian identity and powers, Nash no longer uses his mechanical Duel Gazer when he Duels; instead, his left eye acts as one. He can travel and teleport between dimensions almost instantly. He can also generate viewing screens connected to various places. Like all other Barians, he has the ability to perform a Barian Battlemorph. He can also perform a Chaos Draw, a power which he also granted to the other Barian Emperors. Unlike the other Emperors, he is shown to be able to perform more than one Barian's Chaos Draw in a single Duel. As the leader of the Barians he is extremely powerful, being able to even break free from the area Don Thousand bound him in after he got sufficiently enraged. He is also able to fire electric bolts, as seen when he attempted to hit Vector with it.

Etymology
His Japanese name "Ryouga" is homophone with the word "superior" and also contains the word "fang"(牙) which may reflects his nickname "Shark" while his surname means "Age of the gods". His English dub name "Reginald" means "powerful ruler" while his surname is corruption of the word "castle".

His Barian name is derived from Eta Ursae Majoris, also known as Benetnasch.

Past life
Originally born as Nash, he was once the ruler of the United Lands of the Poseidon Ocean alongside his sister, Marin and was well-loved by his people. One day, his kingdom was attacked by Vector, who led a fleet of ships and several "Gorgonic Guardians" to lay waste to it and loot it. Nash ordered a counterattack, arming his soldiers with mirror shields which turned the gorgons' abilities against them. Vector performed a blood sacrifice in response, calling forth the ocean god, Abyss, turning the tide of the battle again. Marin rode up to Abyss and was grabbed by him. Despite the intervention of Nash's friend, a knight named Dumon, Marin did not want to be saved and sacrificed herself to call forth another god to purify Abyss.

After Marin's funeral, Nash declared an attack on Vector's kingdom in retribution, as the latter has fled with the god turned to Nash's side. Once they got to a town ravaged by Vector's army, Nash noticed a little girl crying, who strongly resembled Marin. Nash took the young girl, Iris, under his care and wondered if she was his deceased sister's reincarnation or if she was sent by Marin herself. As Nash and his army pursued Vector, Nash grew close to Iris and planned to confront Vector by himself once the battle started. On war front, Nash followed Vector to a secret tunnel in what would eventually become a Number ruins, where Vector challenged him to a Shadow Game. Per the Duel's rules, the more monsters of either ruler that were sent to the Graveyard, the more soldiers their army would lose. Though Nash was victorious, his entire army was lost due to Vector's mill strategy. Their souls were sent to the Barian World. Vector barely survived and limped back to his own country, prompting Nash to follow him. There, he found Vector had killed all of his own people. He also witnessed Vector being draggged to the afterlife by the people he murdered.

An unknown number of years later, Don Thousand reincarnated both he and his sister as two of the Seven Barian Emperors, as their souls were each connected to a Mythyrian "Number" card, which had sealed Thousand's power. Nash then became the leader of the Seven Barian Emperors, much to Vector's disdain (also having been reborn as a Barian Emperor). After Nash had annoyed him enough to score 100,000,000 (1,000,000 in the dub) points, Vector enacted his revenge by taking Marin hostage. When Nash intervened, Vector used "Giant Sky Sword" to open a bottomless rift. He then pushed Marin from the cliff, forcing Nash to follow after her only for the two to be sucked into the rift. The two were rescued by Abyss, who informed them that he would send them to the Human World without their memories, where their souls were then revived in the bodies of Reginald and Rio Kastle, who had recently died in a car accident. While Vector believed them dead, Dumon believes they had simply disappeared and assumed leadership of the group from them in the interim, waiting for their return.

Current life
At another time, Reginald and Rio visited a theme park. While there, Rio obtained a pair of matching rings they could wear together. Reginald refused her offer to wear one, and she walked off in anger, calling him an "idiot" and tossing the rings to the ground.

Years later, Rio was critically injured in a fire, while Reginald became a well-known and popular Duelist within the National Duel Circuit. After making it to the final round, the pressure got to Reginald's head, causing him to become desperate because he wanted to win to support Rio. By this point, he began wearing both of the rings that Rio had obtained when they were children, in order to remind him of their bond. While preparing for the finals in the waiting room, he noticed that his opponent, Quattro left and dropped his Deck. While not intentional, Reginald's desperation got the better of him and ultimately looked at the visible cards on the floor. Midway through his Duel, while neither Duelist had a visible advantage, Reginald was disqualified and the match was canceled, as he was discovered to have looked at his opponent's cards. This also caused him to be permanently banned from the Duel Circuit.

After this ban, Reginald became a delinquent and began to steal the Decks of his opponents once he beat them. It is known by most students within Heartland Academy that Reginald was not only a skilled Duelist, but also a bully. He obtained the nickname "Shark", due to the fact that he used an ocean-themed Deck and because he ripped his opponents' Decks out of their hands swiftly and with malice. Despite Shark's actions, Yuma Tsukumo defended him, as he believes that everyone has done something in their past which they regret.

Pre-World Duel Carnival
Shark defeated opponents at his school, taking their Decks after they lost. After defeating Bronk Stone, he met Yuma Tsukumo, who attempted to defend Bronk. When asked what his most important thing was, Yuma told him it was his pendant. Shark ripped the pendent from his neck and threw it away. Shark challenged him to a match, with both Yuma's and Bronk's Decks on the line. Yuma accepted.

They Dueled in the city square, with Shark quickly gaining an advantage with "Big Jaws" and "Aqua Jet". He cornered Yuma, but then the "Numbers" were released from the door. Shark was possessed by "Number 17: Leviathan Dragon", which he proceeded to Xyz Summon. As the Duel progressed, Shark began to toy with Yuma, taking his Life Points down to a small fraction. However, Yuma managed to come out of this with the help of Astral, and managed to defeat Shark with his "Number 39: Utopia" at 5000 ATK, which knocked Shark out. When Shark awoke, he gave Yuma Bronk's Deck, keeping his promise. Shark said that Yuma was different than everyone that he has faced before and walked off without another word (in the dub, Shark says "You may have a point till then, Yuma").

Sometime after the Duel, words of Shark's defeat spread around school and his reputation dropped. Eventually, he stopped going to school and also quit Dueling, and was taken in by a gang led by Scorch and Chills, who hung out at an abandoned arcade. One night, Shark was riding on his motorcycle, and stopped after seeing Yuma, staring at him before riding off. One day, while Yuma was late to school, Shark drove across a road on his motorcycle and nearly hit Yuma. After Yuma is belittled by his friends who believe that his victories over Shark and Flip were just because of his "Numbers", he decided to find Shark and challenge him to a rematch, without using the help of Astral or his Numbers. When Scorch and Chills nearly hurt Yuma and his friends, but Shark told them to stop by saying he knows them. After the gang let Yuma go, he challenged Shark, he refused to Duel as his previous loss to Yuma caused him to give up Dueling. Yuma proceeded to chase Shark and annoy him by requesting a Duel until he accepted, Yuma bet Emperor's Key on the result. Yuma did not use his "Numbers" and Shark told him to do so, believing a victory over Yuma without "Numbers" would be meaningless. Yuma Summoned "Utopia", which Shark weakened with "Friller Rabca". This let "Black Ray Lancer" negate its effects and destroy it, which impressed Astral. Shark won with a direct attack from "Submersible Carrier Aero Shark". Shark took the Emperor's Key, but threw it on the ground as he walked off after he remember what Yuma said about being friends. Before driving away, Shark told Yuma that Scorch and Chills gives him a place to belong and told him not be bother him again.

Shark soon overheard Scorch and Chills' plot of raiding the Heartland museum in hope of trying to steal a valuable Deck containing "Chaos End Ruler - Ruler of the Beginning and the End". He also shocked to discovered that both thugs were possessed by "Numbers". When Chills and Scorch found Shark listening on their plan, he was forced to go along with them, even though he knew this plan was dangerous. Before going, he tells another gang member, Weasel, to run so he doesn't become involved in the dangerous raid, but Weasel went and warned Yuma of the situation instead. Upon arriving at the museum, they found Yuma standing in their way, not allowing them to pass without beating him in a Duel first. He was shocked when Yuma bet his "Number 39: Utopia" on the Duel. Shark warned Yuma not to be concerned for him, but Yuma said he won't leave him alone to rob the Deck. Yuma also pointed out that Scorch and Chills were using him, and that their hideout is not a place for him and insisted that he and Shark were comrades. Shark then decided to Duel with Yuma against Scorch and Chills in a 2-on-2 Tag Duel. On his first move, he Xyz Summoned "Submersible Carrier Aero Shark" and managed to deal effect damage to Scorch. Scorch Xyz Summoned "Number 61: Volcasaurus" and activated its effect, which destroyed "Submersible Carrier Aero Shark" and dealt Shark damage equal to the ATK of "Aero Shark".

Having all their moves countered and with the appearance of "Number 19: Freezadon", which gave "Volcasaurus" its Overlay Units back, Shark and Yuma were pushed into a corner. After Summoning "Utopia" and having it rendered unable to attack by Chills' "Avalanche", Yuma used its effect to protect Shark from attacks which would have caused Shark to lose. After having "Utopia" and the newly Summoned "Black Ray Lancer" destroyed by "Volcasaurus" (avoiding losing by "Damage Diet"), Shark narrowly avoids losing from a direct attack by using the trap "Final Offering", ending the Battle Phase and giving Yuma "Armored Xyz". After eliminating Chills by forcing him to use his "Compensation Exchange" Trap, which saved "Volcasaurus" by taking damage equal to its ATK, Yuma used "Monster Reborn" to bring back Shark's "Black Ray Lancer" and equip it with the "Armored Xyz" Shark had entrusted to him earlier. It allowed him to give "Lancer" the properties of "Utopia", letting it destroy "Volcasaurus" and attack directly for the win. Afterwards, Shark commented that his card was able to improve Yuma's game, allowing him to keep it before smiling and walking off.

When Tori was trying to ask people about the "Number" cards, she ran into Shark, who told her that she should not get involved with those cards and that they are things that neither of them should understand in detail. One day at school, Shark saw Yuma running through the hallways and was amused by it, commenting how "hot headed" he is. Mr. Kay appeared in front of him, expressing his relief Shark returns to school. He shrugged him off and started to walk away, but stopped after he mentioned how much Shark changed after meeting Yuma. Shark listened to Mr. Kay describing Yuma's "sun-like" power, but keeps his cool when asked his opinion and walks away. On the roof, Shark pondered what Mr. Kay said about Yuma, causing him to smile. Seeing Orbital 7 under a trash can moving underneath him and follow it to the boys' locker room in the gym. Shark witness Orbital 7 attempted to steal the Emperor's Key, but he retrieved it and was chased around the school by the robot.

Just when Orbital 7 was about to kill him with a drill, Kite Tenjo stepped in and called a halt. Shark and Kite both chatted a little about their connection to Yuma, and Shark refused to give Yuma's key to him. After hearing Kite mention the "Numbers" cards, Shark realized he is the "Number Hunter" and then lied to Kite about having a "Number" card, then a Duel is started over the possession over Emperor's Key. Shark was confident about his Deck's new Anti-"Numbers" strategy, which proved effective against Yuma. However, he still wanted to have a "Number", so he planned to steal Kite's "Numbers", but Kite noticed it and used "Number 30: Acid Golem of Destruction" so that its negative effects damage Shark when he steals it. Shark remembered that Yuma would never give up, grasped the key and continued the Duel. When Shark lost, he apologized to Yuma being that he failed to protect the Emperor's Key. Shark's soul was taken by Photon Hand, causing him to he age considerably and become comatose. However, Kite was surprised that the soul didn't possess a "Number" card, but still took his soul when Yuma arrived.

Shark was then maintained in the hospital, being look after by Mr. Kay. After Astral and Yuma draw with Kite in a Duel, he decided to release Shark's soul as he wasn't a "Number" holder. He awoke in the hospital afterwards and was told by Mr. Kay that Yuma saved him.

World Duel Carnival Preliminaries
At the beginning of the World Duel Carnival, he met Yuma, who was panicking because he didn't have a Heart Piece. When he was asked if he would be participating, Shark replied he didn't feel like it. When he drove down the road a bit further, he caught a thrown "Mirror Force" card, the card that Shark associated with his ban from the National Circuit, and it turned out to be Quattro, his opponent in his last pro Duel. Quattro explained he purposely put his Deck where Shark could see it, to get him disqualified.

Quattro also revealed that at that time Shark was not only affected by the pressure of the Finals, but also because of a promise he made to his sister who had an accident and was hospitalized, so he was easily tempted to look at Quattro's Deck,.Quattro also says that maybe his sister's accident was not really a coincidence. Infuriated, Shark demanded to Duel with him again, but Quattro told him to wait for the WDC and tossed him a Heart Piece before departing. Shark then decided to participate after all, to get his rematch with Quattro. He fell into Quattro's trap again as Vetrix told him to coerce Shark into participating in the carnival.

After Kari Tsukumo ordered Yuma to find Charlie McCay, he overheard a crowd cheering. Knowing that it would be a Duel, Yuma ran over to see Shark defeat an unknown Duelist with "Submersible Carrier Aero Shark". After the Duel, Yuma congratulated Shark and asked him why he had decided to enter the WDC. Shark told Yuma about how Quattro had mistreated his sister into the hospital to trick him into being kicked out of the nationals, and now he wants a rematch with Quattro, but after that, he will quit the WDC. Shark then told Yuma not to get involved with him and then wandered off, vanishing from sight of Yuma and Tori.

During the second day of the WDC, after Quattro defeated Bronk and Caswell in a Battle Royal Duel, Shark charged into the area on his motorbike, asking him if he remembered the face of his "Number one fan". Quattro agreed to Duel Shark, but Trey snared Shark with his Duel Anchor, preventing the Duel and saying that Vetrix's orders are absolute. Quattro left in a cloud of dust. In the proceeding Duel, Shark takes control of Trey's "Number" monster, "Number 32: Shark Drake". The "Number" pierced his claws into Shark's chest, but Shark's strong will and connection to Yuma overcame the power of the "Number" and he used it to defeat Trey. Trey told him to keep the card and gave him a Heart Piece, revealing that he himself already had a completed heart. When Shark was about to leave, he once again told Yuma not be get involved with him and rode off. Although he was able to withstand the "Numbers" by remembering his time with Yuma, Shark still wanted his revenge against Quattro for his sister, which allowed "Shark Drake" to infect Shark with a small virus (blue in the dub) that will amplify that darkness even further. According to Vetrix, this will help them with their plan to use Shark.

When Yuma, Tori, and Astral were looking for Hart Tenjo, Shark saw them from the road above them and stopped. He overheard Yuma calling out for Kite with his D-Gazer, leaving him wondering about situation. During the third day of the WDC, Shark continued to collect Heart Pieces and brutally defeating many Duelists as the power of "Number 32" began to exert its influence on him, fueling his desire for revenge even more. He was confronted by Yuma, who let Shark take his anger out on him in a Duel. Realizing this, Shark eventually came to his senses, with the darkness of the "Number" disappearing and cancelled the Duel. Before he walked off, he told Yuma that they would meet in the finals and gave him a smile.

World Duel Carnival Finals
Shark attended the party that Mr. Heartland threw for the finalists, but he spent the entire time outside the building. He turned to leave when Quattro caught a glimpse of him through a window. Quattro ran to confront him, with Shark turning his back and telling Quattro he will gamble with everything he has in order to defeat him. After that, he left the party and rode off on his motorcycle. The next day, the Duel Coaster began, and Shark easily defeated an opponent with "Jawsman" before seeing Quattro Dueling another Duelist on a nearby track. Quattro told him that he was fighting magnificently, which Shark vowing not to let Quattro get away and chased after him after the latter defeated his own opponent. The chase continued into the underground section of the Duel Coaster, with Shark and Quattro both defeating opponents and taunting one another. Quattro used Shark's anger against him by leading him toward the Magma Field. Since Shark's Deck was composed of WATER monsters, he would be at a disadvantage.

Shark was prepared to counter the field, "Magma Field", using cards such as "Plate Salvage" and "Adapt to Adversity". He brought out "Submersible Carrier Aero Shark" on his first turn, inflicting 1200 damage to Quattro before he takes his first turn. Quattro countered with "Number 15: Gimmick Puppet Giant Grinder", which Shark countered with "Number 32: Shark Drake". Vetrix appeared, revealing that he intended to use Shark as an assassin to defeat Dr. Faker. Shark insisted that won't happen, with Vetrix responding that he'll have no choice - he will become Vetrix's puppet. After Quattro managed to Summon "Number 40: Gimmick Puppet of Strings" and using the effect of "String of Destiny", Quattro attacked Shark a total of eight times. Quattro revealed that he had been manipulated by Vetrix and that Shark's sister was hospitalized as a result of a fire caused by "Flaming Hell Blessing". Shark told him not to act like he was the victim, even if he was used by Vetrix, Quattro was still responsible. Quattro Summoned "Number 88: Gimmick Puppet of Leo", which would let him declare an Automatic Win on his next turn. Vetrix advised Shark to accept "Shark Drake" in order to win and have his revenge. After some resistance, Shark gave in to and was able to create "Number C32: Shark Drake Veiss" as a result. He defeated Quattro, with Vetrix musing that now he and Shark are friends, mocking Yuma's spirit of "kattobingu". Quattro apologized for hurting his sister and urged Shark to defeat his father and save him. Quattro also added that if Shark wanted to hate someone, he should hate Quattro, not Vetrix. Shark watched as Quattro departed through a portal and talked with Yuma. Now wanting revenge against Vetrix as well, Shark told Yuma he would not forgive him if he got in the way. He boarded his Duel Coaster and moved on, having advanced to the semi-finals.

After defeating Quattro, Shark exited the area on his motorbike, thinking about what Quattro had told him. While driving down a desolate road, he called out for Vetrix so that he could get his revenge (this scene is cut from the dub). Vetrix appeared, right in front of Shark's path, which Shark tried to stop his bike, but failed to do so. Thinking he ran Vetrix over, he got off of his bike to look, but it was merely a hologram. He then spotted another hologram of Vetrix and followed it until he was lead into an abandoned warehouse. Vetrix sneaked up behind Shark and put his hands over his eyes; using his crest's power to put him in a trance. Vetrix then put his hand into Shark's head to gain control of his mind for the upcoming Duel with Yuma. He also gave Shark a powerful Trap Card called "Heraldry Catastrophe" to use in the Duel.

Shark turned up for the finals at the Duel Tower for his Duel against Yuma, but, because of Vetrix's powers, Shark was emotionless. This affected his Dueling as Yuma was able to gain a massive advantage over him by his second turn. However, this was short-lived as Vetrix then began to show Shark visions of Yuma and Dr. Faker causing his sister, Rio to be hospitalized. With a dark revenge in his heart, Shark began to relentlessly attack Yuma with his "Spear Shark" and "Double Shark" in combination with "Zeus Breath", dropping Yuma's Life Points in an instant. He then managed to Summon "Number 32: Shark Drake", cornering Yuma further while the power of Vetrix's crest glowed on Shark's hand. At the climax of the Duel, Yuma took control of "Shark Drake Veiss", causing Vetrix to lose his hold on Shark. Vetrix was about to establish the same control over Yuma, but Shark came to his senses before it could fully happen. Vetrix appeared before Shark and tried to convince him to save Yuma by using his Set "Heraldry Catastrophe", but Shark refused to submit to Vetrix again, and instead used "Underwater Snow Prison" to banish "Shark Drake Veiss" at the cost of the remainder of his Life Points, conceding victory to Yuma. Afterwards, Shark thanked Yuma for rescuing him and encouraged him to defeat Vetrix. Due to his injuries, Shark is then carried away via helicopter to be treated. During Kite's Duel with Vetrix, the latter revealed that Shark was merely a pawn alongside his progeny and Dextra in order to bolster his "Number 69: Heraldry Crest" with rage and hatred as he had no emotions to spare.

Near the end of Yuma's Duel with Vetrix, Shark awoke, witnessing the Sphere Field through the window of the hospital. He watched the remainder of the Duel with Vetrix on television, worrying about Yuma. After it ended, he escaped the hospital and rushed to the stadium, witnessing the explosion of the Duel Tower and the Sphere Field moving towards Heartland Tower. Heading there, Shark encountered Tori, Kite, and Orbital 7. He helped Kite escape from rubble that had fallen on him, and told them his reason for being here. After some arguing, the four agreed to work together and headed to the Sphere Field, but they are stopped by Mr. Heartland, who deployed an army of litterbots to stop them. After Orbital destroys a few, Shark, Kite and Tori wielded fallen litterbot weapons to destroy more of them. When Astral rescued Yuma from the Sphere Field and gave him "Utopia" and "Shark Drake", Yuma returns the latter card to Shark. The three Duelists confronted and challenged Dr. Faker, holding their ace cards high.

As the Duel with Faker began, Shark began to bleed from his stomach from when a litterbot slashed him with it's scythe (the blood is cut from the dub). He however continued on, managing to Xyz Summon "Shark Drake" as well as protect Yuma's "Utopia" via the Equip Spell Card, "Shield Fin". This strategy enabled the three to inflict 5600 damage to Dr. Faker despite the effects of Faker's "Number 53: Heart-eartH". However, Kite mocked Shark for carelessly attacking Dr. Faker without thinking of the consequences, as he received 1400 effect damage from attacking with "Shark Drake". When they thought Kite had defeated Dr. Faker, Shark was shocked to see Dr. Faker had Summoned another "Number" in place of "Heart-eartH".

As the Duel continued, Faker's new "Number", "Number 92: Heart-eartH Dragon" continued to torment the trio, even banishing Yuma's "Number C39: Utopia Ray". When it comes to Shark's turn, Dr. Faker avoids losing via a direct attack from "Shark Drake Veiss" through the "Fake Life". After Shark ends his turn, he falls to the floor in pain as the injury he sustained was worsening. As Kite began his turn, Faker's "Number" banished Shark's "Shark Drake Veiss" and Set card, but while they were being banished, Shark laughed, which shocked Faker. This was because he tricked Faker as his Set card was "Xyz Dimension Splash", which allowed him to Summon two "Hyper-Ancient Shark Megalodon" from his Deck. He then allowed Kite to use them as Overlay Units to Xyz Summon "Neo Galaxy-Eyes Photon Dragon" which reduced Dr. Faker down to 150 Life Points. After the attack, Dr. Faker came clean about his actions and why he committed them. After revealing that Vector was the one which ordered him to do such things in order to save Hart, Yuma, Kite and Shark decided to go after Vector. However, at this moment, Vector emerged from a portal and possessed Dr. Faker, continuing the Duel by resurrecting "Heart-eartH Dragon".

When Hart freed Astral, letting him and Yuma merge, Shark's "Shark Drake Veiss" was used to boost Yuma's "Utopia Ray" and help defeat Vector. When the Sphere Field Cannon began to explode, Shark pushed Yuma out of the way of a piece of falling rubble, injuring himself further. Orbital 7 was reactivated and got Hart, Shark and Tori out of the place. After Yuma and the others reemerge, Shark is taken to the hospital in a helicopter piloted by Nistro, while Dextra administered first aide. During Kite and Yuma's Duel, Astral mentions that Shark should be able to see Astral due the results of the Duel with Vector. During Yuma and Kite's rematch, Shark was able to leave the hospital (although his chest was heavily bandaged) and witness their Duel. He looked on from a bridge with a smile, muttering "Yuma, Astral" before riding off on his bike (the scene showing him leaving is cut from the dub).

Barian Invasion
One day after school, Shark went to visit Rio in the hospital, but ran into Yuma on the way, who suggested they Duel. Shark apologizes and declines Yuma because told him he had to go see Rio, then he sensed the arrival of Girag. Getting an urgent call from the hospital about Rio, Shark rushed there with Yuma and Tori to find Rio crying out in pain. The doctor told Shark that Rio's condition had worsened thirty minutes prior. Rio claimed that disaster was coming and that "they" were coming to take the most important thing, though Shark was confused who are "they". Yuma was called away to save his friends from Fender, Shark attempted to follow, but Rio clutched his hand and stopped him. Later, Shark eventually left the hospital and intercepted part of Fender's gang, while Kite intercepted another part of it. The two defeated all of them and then arrived at Heartland Academy to inform Fender of his gang's failure and give his support to Yuma to battle against the Barian World.

While leaving school, Shark was approached by Art Stanley, the founder of the Comic Book Appreciation Club, who wish to used him as model for his comic. He showed Shark his hero character designs that he had based off of Shark, but Shark shrugged him off. When visiting Rio, he gave her one of the rings from their childhood, unknown that Art was spying on him. When Shark heard that Rio's operation was successful, he went to get her when she was discharged, but was met by Art again. Art informed him that he had his sister and that they would have to Duel. Unbeknownst to Shark, Art was working for the Barian World, having become Girag's most recent pawn. When Shark attempted to counter one of Art's moves with "Zeus' Breath", Art threatened Rio and Shark chose not to activate his card. Wanting to face a "Number", Art gave Shark the components he needed to Summon "Shark Drake", which Shark did. Art countered this by Ranking Up his "Comics Hero King Arthur" into "CXyz Comics Hero Legend Arthur". As Shark remembered the rings from his sister, the power of their bond shattered the Barian's magic and Rio was freed. The bandages flew off of her face and she insulted Shark's Dueling skills as soon as she opened her eyes, to his irritation. Now able to Duel at his best, Shark defeated Art with "Number C32: Shark Drake Veiss". Shark then reunited with his sister and carried her away. Later at school, Shark was shown a samurai-drawing of himself by Art, but he still displayed little interest in it and walked off.

As Rio began to return to school, Shark left their house without her and rushed to school. Despite trying to remain unseen, he met up with Yuma, who asked him what's wrong. Shark began to explain what was wrong, but was interrupted by Rio's arrival, with her calling him mean for leaving without her. Later, Shark ate lunch with Rio, Yuma, and his friends atop of a roof, although Shark sat apart from the group. When Rio started to talk about him, Shark cut her off and yelled at her, but stopped once Rio glared at him. After seeing a group of boys and Bronk smitten with Rio, Shark warned them that Rio is an "ice woman" and they will find out what he means soon. Later, Shark secretly watched Rio Duel against Lotus Hanazoe and goes to her after she wins, calling her Duel "so-so" and asked if she needs any advice from him. While walking home, Shark talks with Yuma about Rio, and then teased her that she hid behind him when she got frightened by a cat, resulting in Rio calling him a "meanie". When Yuma held a "Friendship Games" as way for his friends and Rio to stop fighting with each other, Shark was somehow dragged into it as well, and reluctantly participated in it. He was paired up with Yuma, and was able to put their team in the lead with his skills in Dueling and sports. However, Shark leaves to go home before he and Yuma could face Tori and Cathy in the final Duel, leaving Rio and Caswell to explain his unwillingness to be in the tournament any longer.

Later, Shark went to the mall with Rio so she could go shopping, but waited for her outside by his bike. When Rio came out, she suddenly entered a trance and talked about a fearsome dragon coming to Earth to destroy the "most important things", which Shark knew to mean the Barians' involvement. Driving through the woods, Shark and his sister arrived to see Yuma Dueling against Mizar, and watched as Yuma become greatly injured and couldn't continue. Shark initially wanted to take Yuma's place in the Duel, but Kite took Yuma's place instead, so Shark watched the Duel with the others and was greatly shocked by Mizar's true power. When the Barian Sphere Cube disintegrated, Shark attempted to catch a falling Yuma, but end up falling off a cliff along with him.

Shark and Yuma survived the fall, but they were heavily injured and were sent to hospital, with Shark spending most of his time reading. While recuperating, Shark observed a depressed Yuma and became irritated by his behavior, even yelling at him one at night when he was having a nightmare. When Yuma was out of their shared room, he noticed the Emperor's Key on Yuma's bed and decided to steal it to lure Yuma into a Duel to help him regain his will. Shark immediately brought out "Submersible Carrier Aero Shark" and "Black Ray Lancer", but Yuma responded with defensive plays, angering him. Shark Summoned "Shark Fortress" and broke through Yuma's defenses, nearly winning. Eventually, Astral appeared to help Yuma out his depression and turned the Duel around, making Shark smiled and graciously lose the Duel to Yuma. Astral pointed out that Shark's reason for doing all that was to help Yuma, though Shark denied it and pushed Yuma away when the latter tried to hug him.

Once he was discharged from the hospital, Shark went to school and heard Rio sensing a Barian presence again and the two rushed to aide Yuma alongside Tori. They found him surrounded by brainwashed Duelists and helped him Duel his way out until Alito arrived and ended the Battle Royal. Afterwards, they watched Yuma begin a Duel with Alito within another Sphere Cube. Later at school, Shark was asked by Bronk to Duel him, who was trying to gain his blessings to date Rio, but Shark declined since he was no match for him. He also added that Bronk wasn't even at Yuma's level, causing Bronk to jump to the conclusion that Rio was with Yuma. Flip and Caswell overheard this and spread a rumor around the school. Oblivious to the rumor, Shark was challenged by an angry Rio to a Duel and accepts after she insulted him. During the Duel, Shark was able to counter every strategy Rio played and voiced little faith in Rio's confidence as a Duelist. While Shark was proud that Rio was able to gain courage, he proclaimed that she still has a long way to go if she wanted to beat him and defeated Rio with his "Shark Caesar". Afterwards, Shark learned the rumor from Rio and cleared up the misunderstanding, clarifying that he wasn't the one spreading the rumor.

During Heartland Academy's Fun Fair, Shark observed the play Rio was acting in and displayed irritation watching her with Yata-Garasu. When Bronk came to him, Shark was shocked by his cosplay as "Gogogo Golem" and grew annoyed that he was calling Shark "brother". Shark's irritation prompted Rio to throw her shoe at Shark and telling him to be quiet or leave. Later, Shark took part in the festival by playing bass guitar alongside his fellow students for the famous singer, Scarlett Starling, much to the excitement of his female admirers.

After "Ray Shadows" was kidnapped by Vector, Shark rushed to Yuma's location and watched his conversation with Kite. Inside Heartland Tower, Shark heard Yuma's explanation, and said that he wanted to go with him to save Ray and find Vector. Shark then bickered with Kite about how to get to the Barian World when the tower shook. They ran to the top to see that the Different Dimension Airship from the Emperor's Key had crushed the top of the tower and was resting there. Astral told them that they could use the ship to get to the Barian World. Later, Shark spoke with Rio about his mission with his friends, and was forced to take Rio along when she wanted to go with him. In the morning, Shark and the group entered the ship and took off, but an array of monsters began assaulting the ship. Shark and the others went to the exterior, using their ace monsters to battle with them until a portal sucked them in. At "Sargasso the D.D. Battlefield", Shark watched Vector taunting a devastated Yuma with Ray's seemingly dead body, when Dumon challenged him to a Duel. Shark was given the first turn and quickly Summoned "Number 32: Shark Drake" and took the damage inflicted by the effect of "Sargasso". Although he was at an disadvantage, Shark was still confident against Dumon and ended his turn, taking "Sargasso's" damage again, even when Dumon brought out his "Over-Hundred Number", "Number 102: Star Seraph Sentry". He also listened to Vector revealing that he was really "Ray" all along and boasting how it was so he could plan Yuma's downfall, which Shark showed visible disgust to.

As the Duel continued, Shark Summoned "Number C32: Shark Drake Veiss", but his Life Points whittle down to 900 due "Sargasso" effect. When Yuma was blaming himself for putting his friends in danger, Shark told Yuma that he came on his own will and encouraged him to win his Duel, but was stunned when Yuma and Astral transformed into Dark ZEXAL. After Yuma undid Dark ZEXAL, Shark helped inform Yuma of his status and paused his Duel with Dumon to watch Yuma and Vector's. Dumon asked him if he still believes that Yuma could win, which Shark said he does because that was trust is all about. After the power surge of ZEXAL II caused "Sargasso" to self-destruct, Shark's Duel with Dumon was canceled, and he returned to Heartland with everyone else.

Mythyrian Numbers War
Later at school, Shark was skipping class when he felt a strong presence of Don Thousand when he was revived by Vector. On the roof, Shark, Yuma, Tori and Rio were brought aboard the Different Dimension Airship by Astral, who informed them of the seven "Mythyrian Numbers" scattered across the world. As they headed to their first location, they ended up crashing into Dumon and the ship landed them into a jungle. After Yuma saved a boy named Nash from a bear, Shark inquired who he is. He didn't believe the mysterious, injured boy "Nash" was just a "traveler" and stated he might be a Barian. Shark told Yuma not to trust the boy so easily, but the conversation was cut off when the group hears Tori's scream from some distance. They ran to a temple where she and Rio were, and had to get rid of the snakes surrounding them. As the group traveled further inside the temple, a trap activated and Shark almost got crushed under a wall, but "Nash" saved him and they were separated from the others. When a door opened up, Shark and "Nash" went down the pathway, leading them to an empty room. Shark thanked "Nash" for saving him, but said he still doesn't trust him, though "Nash" shrugged it off and said he did it in return for Yuma saving him. When the walls started to close in, they were captured and their lives depended on the outcome of Yuma's Duel with Mach. Shark and "Nash" were forced to work together to survive the collapsing and changing labyrinth. Following Astral's instructions, they tried to interpret the ruins' legend of a hero and his pegasus in order to find a clue to help Yuma win the Duel. Shark suspicions of "Nash's" identity deepens when the latter revealed he could translate the legend. When the floor collapsed, Shark was about fall into the hole, but "Nash" was able to grasp his arm. When their hands touched, Shark began to glow and "Nash's" Baria Crystal was repaired, revealing "Nash" to be Dumon. Although Dumon saved him, Shark urged Yuma not to trust Dumon and to destroy "Number 39: Utopia" instead of protecting it. Using Dumon's advice, Yuma was able to win the Duel and allowed a door to open for Shark to regroup with them.

Going to South America, Shark and the others arrived at an abandoned castle, and listen to Rio speak of legend about a ruthless prince. After Yuma accidentally triggered some traps, Shark and everyone else ended up inside the cages of the central colosseum. With Vector and Number 96 focusing solely on Yuma and Astral, Shark was forced to watch Astral Duel Number 96 and worried about Yuma, who has a giant pendulum axe aimed at him. After Astral tied with Number 96, Shark and the others were released from their cages and escaped the crumbling ruins. The group then headed to Spartan City, where Shark and friends went to see the Pro Duelist Spartancity Tournament and reunited with Nistro and Dextra. They learned the tale of a warrior from the duo and deduced that "Number" was in the coliseum, which was under a lake. At night, Shark and the others were awoken by explosion coming from the ruins and rushed over there. When Yuma and Dextra began a Tag Duel against Alito, who brainwashed Nistro, Shark watched the Duel alongside Kite and Rio. After the Duel ended, Shark and the others returned to the airship the next day and listened to Tori and Orbital 7 complaining to Rio about being left behind.

On the way to the next location, Shark spoke with Yuma about his daze and knew he was thinking about Alito. Shark told him that Alito's change in personality exposed his "true colors" as a Barian and was annoyed by how Yuma still seemed so concerned about him. Upon arriving in an mountain range, Shark went with Yuma and Kite to climb a mountain to reach the ruins. As he was struggling to climb, Shark snapped at Yuma, who was giving them pointers to mountain-climbing, and told to shut his mouth. When they came to the Number ruins, they met Jinlon, a Number Guardian. Shark listened to Jinlon and Astral's conversation about the person similar to Kite, which the former confirmed the person was named "Mizar". Astral revealed to Shark and the others that the Barians were humans once, but Shark found his statement ridiculous. Shark then watched Kite Duel against Jinlon along with Yuma and Astral. After Kite won the Duel, Shark and the others listened to Jinlon's tale about Mizar and how he died. When Mizar arrived at the ruins and clashed with Kite's dragon aura, the group ended up on a mountain peak after the Number ruins vanished. They listened to Jinlon explaining that when people searching for "Numbers" come to the ruins, huge changes will occur in the world and about the "two lights" battling in the sky long ago.

As the Different Dimension Airship headed to the final two Number ruins in the ocean, Shark overheard Yuma and Astral speaking about the Barians about being humans. He warned the duo that over thinking the situation was a bad idea and they should not get emotions involved. Yuma asked Shark's reason for fighting against the Barians, he replied that what the Barians done to him and Rio was enough for him to seek revenge. When Yuma mentioned Shark forgave Vetrix and Dr. Faker for their transgressions, Shark clarified he never did forgave them and that he only stopped fighting them because they lost the will to fight. Astral inquired not involving emotions in a Duel was Shark's philosophy, but he stated that he was fighting for his own sake and proclaimed himself a "lone wolf". In the midst of a storm, Abyss possessed Rio and Shark witnessed her plunging into the water below and quickly followed, with Yuma and Astral close behind. Following Rio's footprints, they entered the labyrinth-like ruin and Shark noticed Rio's "Freezing Point" card lying on the ground and went to examine it, but the labyrinth suddenly generated new walls to separate them. Shark eventually reached the heart of the temple and found still Rio possessed by Abyss. Abyss claimed he and Shark were destined to fight and urged him to "awaken", as he is the one who will inherit Abyss' powers. Shark began a Duel to get Rio back, but Abyss gained a significant advantage over him with "Gorgonic Guardian". Abyss used his powers to allow Shark access to his past life's memories and he recalled Vector's attack on his kingdom and expressed confusion over the whole situation.

As he continued to see visions of his past, Shark defeated "Gorgonic Guardian" by turning its own effect against it with Rio's "Freezing Point" card, reflecting how it was defeated in the past with mirror shields, but Abyss brought forth the "Number 73: Abyss Splash. After Shark saw how Rio had died in her past life, Abyss insisted that Shark would lose his sister and everything important to him in this life just as in the past, saying it was because of the weakness in Shark's heart. When Abyss released his control over Rio, Shark was able to contact the other "Number" in the ruin, "Number 94: Crystalzero". Using the "Number", he defeated Abyss and entrusted both "Numbers". Afterwards, Shark and the others was transported back to the airship, but Rio remained unconscious.

Returning to Heartland, Shark visited his comatose sister at the hospital when she had another premonition, saying a great darkness was surrounding Yuma and that a great tragedy would soon happen. Worried, Shark rode off to find Yuma with Tori and asked if Yuma was alright. As ashes began to fall from the sky, the group was transported by Number 96 to another location, alongside Kite and Orbital 7. Shark and group listened to Number 96's goal of destroying all three worlds and observed Yuma Dueling against Number 96. As events came to a climax, they witnessed Astral destroying Number 96 and forced to parted ways with a tearful Yuma. Shark and the others were transported back to Heartland and stood silently as a heartbroken Yuma cried for his lost friend. Sometime later, an anguished Shark visited Rio again when Tori also came by with flowers. She tried to talk to Shark about Yuma's current painful state, but he told her that things are already bad and that he does not want to talk to Yuma now because he doesn't know what to say to him and doesn't know how to. After Tori left, Shark reflected how the "current [him]" had done and said everything he could say and do, but wished that there was a chance to fix everything.

As he continued to visit Rio, Shark struggled to accept what he had learned in the temple, causing him to think of his own past and the death of his parents. When Shark returned to his old house and reflected on the memories of his childhood, he determined he couldn't be a Barian. Suddenly, he was ambushed by Chironex, who attempted to sting Shark with jellyfish poison, chasing Shark out of the house. Eventually, Shark was infected by the poison and Chironex wagered the poison's antidote on a Duel, pointing out they had already infected Rio as well. When Quattro intervened, calling himself Shark's "biggest fan", Shark was shocked to see his old rival and stubbornly rejected his help. However, with poison quickly taken affect on his body, Shark grudgingly teamed up with Quattro to Duel Chironex. After the Duel, Shark learned that Chironex was responsible for the car crash and stated that even Shark died, which confused him. Shark then noticed that a fountain in the backyard of the Kastle's mansion had the same crest that his past life did, making him realize that his entire family are descendants from his past life. With his previous resolve shaken, Shark wondered if he really was a Barian.

At the hospital, Shark reflected on what he had learned after his duel with Chironex, especially about how he and Rio were supposedly killed in the car crash. When he turned around he was shocked to see Dumon, who called him "Nash" and told him it was time to realize his identity. Shark and his comatose sister were transported back the Number ruins by Dumon and he experienced more memories of his past life. As Shark experienced his past life's events, Shark met Rio's spirit, who told him that she was also watching those memories. They spoke about the war and how Shark will choose a kind decision to minimize the causalities, even if he will suffer from it. Shark told Rio that he remembered that someone taught him how hatred would spread if he didn't, and smiled once Rio correctly guessed that "someone" was Yuma. After Shark saw how tragic the war between Nash and Vector ended, Shark accepted that he was indeed a Barian and he was Nash. Dumon stated that the Barian World originally did not have many residents in it due to the actions of Astral World, but Shark's legendary battle with Vector caused all the perished souls to enter the Barian World; that connection alone was why Shark was the leader of the Seven Barian Emperors. With bitter tearful eyes and his sister trying to comfort him, Shark lamented on how destiny can be so cruel and ironic, realizing that the enemy Yuma, Astral and Kite should be fighting is him.

Shark and Rio were then transported to the Barian World and found Nash's army and Iris, who warmly greeted him. Shark listened to Dumon telling him that he was the only one who could end the war with Astral World, even if it meant breaking his bond with Yuma and his friends. As Shark remembered his times with Yuma, his friends and rivals, Shark ruefully chose to follow his destiny and settle the war his way, accepting his identity as the Barian, Nash. Later, he told Rio to stop calling him "Reginald". Rio called the entire situation her fault, as none of it would have happened had she not sacrificed herself in her previous life. Shark responded that it was he that was to blame, as his hatred of Vector in his own past life was what started this. She asked if he could really fight Yuma and his friends and Shark responded that he would, "for the sake the Barian World", while throwing away the pendant that contained the picture of his family. They regained their original Barian forms and assumed control as leaders of the Seven Barian Emperors once more, calling for an emergency meeting. Vector was shocked to see that Nash and Marin had returned and were still alive. Dumon revealed that they ended up on Earth as humans. Nash confirmed that though they were enemies in the Human World, he was on their side now. To prove this, he told Vector to kill him should Vector sense any hint of betrayal. Vector suggested they attempt to take Earth immediately, as Yuma and Astral aren't around. Nash told Vector not to underestimate Yuma - there is no way he won't be back. He bestowed new power to each of the Barian Emperors, then agreed to Vector's plan.

Barian Emperor Onslaught
After Mr. Heartland was defeated, the Seven Barian Emperors arrived together on Earth in front of Yuma, who was pleased to see Shark. Shark responded that he was no longer Shark or Reginald, but Nash of the Barians. The seven proceeded to Barian Battlemorph and revealed that he was the leader of the Barians. When Yuma asked why that had to battle, Nash responded that this is what fate had decided, which Yuma found to be ridiculous and promised to revive their bond through Dueling. Suddenly, his Barian Emblem reacted with the Emperor's Key, letting Yuma see Nash's past life and Nash see the events that Yuma had been involved with in the Astral World, making him comment that they both carried the responsibility of a world on their shoulders. After Yuma fainted, they were about to attack when Roku and Kaze arrived and pelted the Emperors with smoke bombs, allowing Yuma's entire group to escape. Nash ordered a chase, but each of the other Emperors except Vector were blocked by Yuma's companions and forced to Duel. Nash caught up with the car they had used to flee and found himself confronted by Quattro as the car sped away again. Quattro vowed to do what Yuma would do - reforge the bonds of friendships with a Duel, but Nash proclaimed they can never understand each other no matter how many times they Duel. Although, Quattro gained the advantage, Nash revealed his "Over-Hundred Number" card, "Number 101: Silent Honor ARK". In response, Quattro used what he called the "trump card of humanity" - "Rank-Up-Magic Argent Chaos Force" - to create "Number C15: Gimmick Puppet Giant Hunter" and destroyed "Silent Honor ARK". Nash then initiated a Chaos Draw at the same time as the other Emperors.

This lets each of them create "Rank-Up-Magic - The Seventh One". Each of them Ranked Up their "Over-Hundred Number", with Nash unveiling "Number C101: Silent Honor DARK". He claimed he was never friends with any of them and urged Quattro to see him not as a friend, but as an enemy he must defeat, but Quattro still aimed to reforge their bonds. Quattro countered "Silent Honor DARK" by using "Argent Chaos Force" to create "Number C40: Gimmick Puppet of Dark Strings". Though it destroyed "Silent Honor DARK", that card was able to revive itself and give Nash more Life Points, to boot. All the other Duels ended with the defeat of the human participants and Nash allowed Quattro see each of them. Finally, Quattro lost hope that he could save Nash and Nash claimed he could bury the last link to "Reginald" by defeating Quattro, but was pleased that Quattro's hatred had been reignited as his voice adopted a more demonic tone. Quattro proceeded to Rank-Up "Number 88: Gimmick Puppet of Leo" into "Number C88: Gimmick Puppet Disaster Leo", but Nash countered its Automatic Win condition by attaching an Overlay Unit from "Silent Honor DARK" to it via "Overlay Award". Using "Cross Draw of Destiny", Nash Summoned "Silent Wobby" to Quattro's field and absorbed it with "Silent Honor DARK", defeating Quattro with a boost from "Power Stream". After the Duel, Nash returned to his human form while Quattro shared his final words with him, pointing out that Nash was using him to force himself into a destiny he couldn't escape from. As Quattro was sent to the Barian World, he remarked he would be going to hell before Nash, who responded that he'd be joining Quattro there as soon as the conflict was over. The other Emperors regrouped and Nash ordered them to split and find the remaining "Number" holders - Yuma, Astral, Trey and Quinton.

Shortly thereafter, Nash was alerted to a Duel starting by seeing "Number 9: Dyson Sphere" in the sky. Girag approached him and informed him that Yuma and his allies were on their way to the Barian World. He ordered Girag to return there quickly, while doing the same himself. Partway through the trip, Girag pretended to be trapped by dark tentacles, prompting Nash to try to save them. The tentacles snared Nash and Girag told him he couldn't be allowed to Duel Yuma, saying it was in the name of Don Thousand.

Within an inflamed Sphere Field, Nash was tangled in dark tentacles, being confined by Don Thousand. A screen appeared before him, letting him witnessed his sister and Dumon being confronted by Vector and Don Thousand. They revealed that the Seven Barian Emperors were created by Don Thousand to serve as fuel for his revival. When the Duel commenced, Vector activated the Spell Card "Don Thousand's Throne", which drew power from Nash, causing him great pain. As the Duel continued, Nash, Marin and Dumon finally learned what happened to the Barian leaders long ago as Vector revealed he killed them and that their souls were transferred into new bodies for them to live on by Abyss, but without their memories as Barians. As Nash continued to watch the Duel, he watched in horror as Dumon was killed trying to protect Marin from Vector's wrath. When Marin was about to be defeated, Nash begged Vector to take him instead, but Marin was killed by Vector in the end as he yelled her name in anguish, calling her "Rio". Marin's spirit appeared to him and called him "Reginald", telling him to live on and that she was glad to have walked the same path as him. When Vector left to absorb the souls of Girag, Alito and Ponta, Nash broke out of the Sphere Field in a rage and resumed his Barian form. This alerted Vector, causing him to leave Yuma as Nash immediately began to travel through the dimensions to find Vector, who had returned to the Barian World.

When Nash arrived, he fired a lightning bolt at Vector in a rage. They began their Duel, with Vector having brought the ruins from his past life into the Barian World to serve as their arena. Vector used "Contract with Don Thousand" to give Nash a handicap, with Nash proceeding to fall into his trap and attack with "Silent Honor DARK" after Summoning it with "The Seventh One". Using a combination of "Chaos Rising" and "Chaos Caller", Vector brought out "Number C65: King Overfiend", "Number C104: Umbral Horror Masquerade", "Number C102: Archfiend Seraph" and "Number C103: Ragnafinity". Yuma arrived to support Nash at this point, but Nash persisted that they were enemies now. Vector used the power he had gained from the other Emperors to gain a new form. Nash survived Vector's assault with 100 Life Points and launched a counterattack using "Split Defender" and "Xyz Charge Up", ultimately resulting in him taking control of "King Overfiend" and using it to destroy "Umbral Horror Masquerade". This triggered Vector's true memories. Once he remembered, Vector claimed to have realized the error of his ways, and activated "Xyz Discharge", allowing Nash to seize control of his comrades' "Chaos Over-Hundred Numbers" at the cost of sending a card in his hand to the Graveyard. Attacking at Vector's wishes, he fell into his trap, "Trick Buster", which destroyed all of Nash's monsters and dealt him 300 damage for each monster destroyed. However, Nash avoided the damage by activating the effect of his "Dream Shark". Vector, who was surprised to see him survive, accused Nash of not trusting him to start with, with Nash responding that he discarded the ability to trust when he shed his humanity. As the battle waged on, Vector performed a direct Chaos Xyz Evolution, Summoning "Number C5: Chaos Chimera Dragon" with the effect of "Rank-Up-Magic Admiration of the Thousands", using "Chaos Numbers" in the Graveyard as Overlay Units. This card nearly defeated Nash, but he survived with "Depth Gardna" and then used "Infinity Tooth" to counter Vector's manipulation of his draws. He performed a second Chaos Draw and used the resulting "Depth Biter" to Summon "Number 73: Abyss Splash". Though Vector countered with "Overlay Burglary", Nash revealed a second "Rank-Up-Magic" in the form of "Rank-Up-Magic Quick Chaos", creating "Number C73: Abyss Supra Splash" and defeating Vector.

As Vector went berserk with his power, Nash was surprised when Don Thousand appeared before them and tried to absorb Vector. He showed a little concern when Yuma ran to try and save Vector, urging Yuma to stop and that Vector had no soul; even if Yuma did save Vector, Vector would backstab him again. After Vector let himself be absorbed to protect Yuma and Don Thousand assumed his true form, Mizar arrived and Nash watched the Duel between him and Don Thousand. When Mizar lost, Nash mourned his death, which left him as the last of the Seven Barian Emperors. With his new form, Don Thousand stated that he will absorb Nash as well and challenged him and Yuma to a Duel. To avenge his comrades, Nash agreed to team up with Yuma against Don Thousand. Thousand quickly negated Yuma's Summon of "Utopia," revealing that the merging of the Barian and human Worlds was to enable him to control the Numeron Code, allowing him to attack the Astral World directly. Using his "Numeron" monsters, Thousand nearly defeated them, with Yuma and Nash surviving with "Half Unbreak" and "Cutter Shark". Astral left to find the location of the "Numeron Network" card to help them. Nash baited Thousand into using "Numeron Network" to rewrite his "Aqua Jet", allowing him to use "Rank-Up-Magic - The Seventh One" to bring out both his "Over-Hundred Number" and its "Chaos" form. Thousand survived with "Numeron Wall", but by then Astral had found "Numeron Network" and put it onto the field, resulting in Nash destroying it with "Depth Eruption". Nash was tearful when it appeared that Astral would sacrifice himself to keep the resulting energy from destroying Earth, but Eliphas appeared and sacrificed himself in Astral's place.

Yuma and Nash worked well together, with their combinations nearly defeating Thousand several times. However, Thousand countered with "Number C1000: Numerronius", whose effects controlled nearly the entire field. Nearly defeated, Kite's spirit appeared to Yuma and Yuma was able to counter with "Number 100: Numeron Dragon". This play forced Thousand into his final trump card, "Number iC1000: Numerronius Numerronia". The card could not attack, but essentially put a timer on the Duel - if they did not attack it next turn, Thousand would win automatically. Yuma activated "Session Draw", letting both of them draw during Nash's next Draw Phase. If the monsters drawn were of the same Level, they could Xyz Summon using them. Yuma used Shining Draw, while Nash used Chaos Draw, allowing them to use "ZW - Tornado Bringer", "Panther Shark" to bring out "Abyss Splash". Yuma's "Utopia Rising" and "Bonds of Hope" Trap Cards further augmented "Utopia" with the effects of "Abyss Splash" and "Numeron Dragon".

This combination of effects seemed to defeat Thousand, but he had one last counter in the form of "Numerronius Numerronia" being able to negate an attack and gain ATK by detaching an Overlay Unit. Yuma's final counter was "Double or Nothing!", enabling "Utopia" to destroy "Numerronius Numerronia". Thousand laughed upon his defeat, and what remained of his power along with his "Numbers" were absorbed by Nash. Still wishing to save the Barian World, Nash transported Yuma and Astral to an arena between the worlds, revealing that the worlds would collide soon, resulting in the Astral World's destruction. Yuma insisted the worlds could coexist, but even Astral told him this could not be, as a merging of all the worlds would simply cause the weakened Astral World to fade away. Nash declared that though he still considered Yuma and Astral his friends, it did not matter - he would fight for the sake of the Barian World, to protect his other friends. He also revealed that Thousand has never cursed Nash as he did the other Emperors - he became a Barian of his own free will, as his comrades had already been sent to the Barian World. He claimed the true curse was his very existence. Nash challenged Yuma to one last Duel with all the "Numbers" - and by extension the power of the Numeron Code - on the line. Honoring his fallen comrades, Nash utilized the "Chaos Over-Hundred Number" monsters of the other six Emperors, even Summoning some of them to Yuma's field.

Nash used the seven "Chaos Over-Hundred Numbers" to Summon his ultimate ace card, "CXyz Barian Hope". This monster wielded the power of all seven of the "Chaos Over-Hundred Numbers" and allowed Nash to use each of their effects once per turn by either detaching an Overlay Unit or paying 400 Life Points. Nash continually paid his Life Points, as he did not wish to sacrifice his comrades again, as their souls were bound to the Overlay Units. Though Nash used the effect of every "Chaos Over-Hundred Number", Yuma and Astral narrowly avoided defeat. Yuma and Astral performed ZEXAL Morph, but at that point, the worlds began to drift closer to one another. They were saved by Kazuma Tsukumo and Vetrix, who used the last of their power to erect barriers between the arena and the colliding worlds. They both urged the Duelists to continue the Duel. Yuma used "Rank-Up-Magic Astral Force" to create "Number 39: Utopia Beyond". "Barian Hope" would have been destroyed, but Nash countered with "Overlay Menace" to protect the other Emperors and "Xyz Trip" to negate the attack. Nash attempted a counterattack, but Yuma's "Weaker Overlay" and "Damage Reactor" allowed "Utopia Beyond" to destroy "Barian Hope". Nash screamed in anguish, asking why Yuma and Astral must keep crushing the dreams of the Barians.

Nash set up the return of "Barian Hope" with "Reincarnation of the Seven Emperors" before Summoning "Black Ray Lancer" in an attempt to defeat Yuma. Yuma countered with the effect of "Utopia Beyond", Summoning "Utopia" again. Nash weakened "Utopia" with "Friller Rabca" and brought out "Submersible Carrier Aero Shark" as well, but Yuma survived with "Damage Take-Over". Using ZEXAL, Yuma and Astral created "ZW - Sylphid Wing", but Nash revived "Barian Hope" using "Rebirth of the Seven Emperors" at the expense of his Rank 3 monsters. Yuma pushed the attack, but Nash used "Draw of Fate" to negate the attack and force both players to draw a card. If the player did not use the drawn card by the end of this turn, they would automatically lose. Nash used Chaos Draw to draw "Glory of the Seven Emperors", while Yuma used Shining Draw to draw "Double or Nothing!" Yuma canceled his attack after activating "Double or Nothing!", knowing that defeating Nash would be to sacrifice who Yuma had been, just as the Door had predicted. Nash had known he would "Double or Nothing!", but this action was not predicted. "Glory of the Seven Emperors" would have allowed him defeat Yuma had Yuma done anything else, but canceling his attack resulted in Nash's Life Points becoming 0. Nash told Yuma never to lose what was most important to him - his ability to believe in others and his pure heart. He mused that he'd not see the future they would create though. The "Numbers" flooded from Nash's body and were absorbed by Astral. Nash told Tori to never let Yuma out of her sight and called Yuma and Astral the best friends he'd ever had. He informed them that he considered this final Duel to be his greatest - and also the most enjoyable. Nash succumbed to his wounds after this, fading away.

After Yuma's and Astral's Duel, Shark, his sister and the other Emperors were revived by the power of the Numeron Code. He continued to attend Heartland Academy with Rio. Upon knowing of a new crisis in the Astral World, they all joined Yuma and headed there in order to help Astral.

Number Hunting
Reginald was the original owner of the very first "Number" to imprint itself on an owner, "Number 17: Leviathan Dragon", which he lost to Yuma and Astral.

Sometime later, Trey gave him "Number 32: Shark Drake" after their Duel during the World Duel Carnival. He would eventually lose this card to Yuma as well, but later regain it after Yuma recovered it from the Sphere Field and allowed him to keep it. He also learned to evolve it into "Number C32: Shark Drake Veiss" just as Yuma had done with his own ace card.

Reginald acquired two of the Mythyrian "Numbers" from Abyss - "Number 73: Abyss Splash" and "Number 94: Crystalzero". He would eventually obtain an upgrade for "Abyss Splash" in the form of "Number C73: Abyss Supra Splash"

After learning of his true origins as Nash, he was able to wield his "Over-Hundred Number" - "Number 101: Silent Honor ARK" and its upgraded "C" form, the "Chaos Over-Hundred Number" "Number C101: Silent Honor DARK". Upon defeating Quattro, he acquired "Number 15: Gimmick Puppet Giant Grinder", "Number 40: Gimmick Puppet of Strings" and "Number 88: Gimmick Puppet of Leo" and possibly their upgraded forms - "Number C15: Gimmick Puppet Giant Hunter", "Number C40: Gimmick Puppet of Dark Strings" and "Number C88: Gimmick Puppet Disaster Leo", respectively.

After defeating Don Thousand alongside Yuma, Nash absorbed all of Thousand's "Numbers". Among them were "Number 1: Numeron Gate Ekam", "Number 2: Numeron Gate Dve", "Number 3: Numeron Gate Trini", "Number 4: Numeron Gate Catvari", "Number 5: Doom Chimera Dragon", "Number 6: Chronomaly Atlandis", "Number 9: Dyson Sphere", "Number 33: Chronomaly Machu Mech", "Number 43: Manipulator of Souls", "Number 46: Dragluon", "Number 58: Burner Visor", "Number 62: Galaxy-Eyes Prime Photon Dragon", "Number 64: Ronin Raccoon Sandayu", "Number 65: Djinn Buster", "Number 80: Rhapsody in Berserk", "Number 96: Dark Mist", "Number 102: Star Seraph Sentry", "Number 103: Ragnazero", "Number 104: Masquerade", "Number 105: Battlin' Boxer Star Cestus", "Number 106: Giant Hand" and "Number 107: Galaxy-Eyes Tachyon Dragon". Many of these also had "Number C" forms, including the "Over-Hundred Numbers". In addition, there was "Number C1000: Numerronius" and "Number iC1000: Numerronius Numerronia", which lacked a base "Number" form.

After losing to Yuma, Nash gave Astral all the remaining "Number" cards before dying, resulting in Astral obtaining all 100 base "Numbers".

Rio Kastle
Shark and Rio are twins and share a strong bond ever since they were children, symbolized by matching rings that Rio obtained. Following Rio's Duel with Quattro, in which she was critically injured and wound up in a hospital bed wrapped in bandages, Shark Dueled in the National Duel Circuit for her sake, but pressure was escalated to such an extent that he peeped at his opponent's Deck before the final match, an action that caused him to be disqualified and banned. During the time Rio was in the hospital to recover from her injuries, Shark often visited her.

Despite their bond, Shark has a typical tenuous "brother-sister" relationship with Rio, irritating one another and having normal sibling squabbles. They seem to settle any fighting by Dueling each other, having a total of one-hundred Duels.

Their bond is incredibly strong, with brother and sister remaining close over many of their lives with Rio supporting and standing by her brother's side ruling together with him as Marin in their original human lives, as well as again after returning to being Barians.

Yuma Tsukumo
Shark first met Yuma Tsukumo when he came to defend Bronk Stone after he beat him in a Duel and took his Deck. In a twist of events, Shark crushed the Emperor's Key and accepted Yuma's challenge, becoming rivals with the young boy. With their Duel underway, Shark was overtaken by "Number 17: Leviathan Dragon" and quickly Summons it to put Yuma in his place. However, with the appearance of Astral and Yuma's new Xyz Monster, "Number 39: Utopia", Shark loses the Duel and his "Number".

Soon after, Shark falls into the "wrong crowd" and stops Dueling all together, but with persistence from Yuma, Shark agrees to Duel him again. Despite his "Numbers", Yuma loses to Shark, who then tells him to never interfere with his life. However, Yuma disobeys this after learning of why Shark was the way he was. The two then have a Tag Duel against Scorch and Chills, also carried "Numbers" that supported each other. Despite that, Shark was able to aid Yuma, who protected him from any damage, and give him the final trump card that would defeat the two brothers. As a sign of respect for Yuma, he allowed him to keep the card he won with.

Mr. Kay made a remark that Shark had changed due to Yuma's influence and now he sees Yuma as a friend and ally. Although friends, Shark doesn't hang around Yuma as much as his other friends, due to his aloof nature, but is shown to have a soft spot for him. In addition, Shark often reflects on his time with Yuma, even watches Yuma from afar when he sees him. Despite his distant nature, Shark is willing to open up to him (to an extent), but tends to push him away sometimes. In turn, Yuma admires Shark and worries about him if he does anything he thinks is wrong or dangerous. When knowing things concerning Shark, Yuma would focus his attention on helping him and putting himself in harm's way, even sometimes ignoring or lashing out on his friends or Astral if they tried to stop him.

Throughout the World Duel Carnival, their friendship becomes strained as Shark became focused on revenge on Quattro and continually told Yuma "Don't get involved with me" when they met. When Yuma learns how violent Shark had become, Yuma challenged him to a Duel, in which Yuma made no move to attack, and let Shark take his anger out on him. He was angry at Yuma's persistence and the Number's influence causes him grow more aggressive. Eventually, Yuma tells Shark he doesn't want to see the way he is now, shocking him, and is followed by his stomach growling. As Shark watches Yuma and Tori shout at each other, he smiled and the darkness in his heart disappeared. Shark then cancelled the Duel, claiming that seeing Yuma being an "idiot" made him lose his drive. Before walking away, Shark tells Yuma that he would meet him in the finals and they exchanged smiles.

During the WDC party, Yuma tried looking for Shark, showing his concern for Shark, and because he has something to ask him, but couldn't find him. During the finals of WDC, Yuma stumbles across Shark's Duel with Quattro and stayed to cheer him on. When Shark Summoned "Number 32: Shark Drake", Yuma worried about him due to the influence of the "Number", and cried out to Shark as he was brutally attacked eight times by Quattro. As the Duel continues, Yuma tried to pull Shark away from the influence of the "Number", but Shark eventually gives into it. After Shark wins the Duel, Shark set his revenge on Vetrix and told Yuma he won't forgive him if got in his way, straining their friendship once again.

In the semi finals, Yuma and Shark were matched-up to Duel each other, with Yuma eager to settle their rivalry. Unknown to Yuma, Vetrix was influencing Shark through the power of his crest, but Yuma does notice how emotionless and different Shark is. During the Duel, Vetrix made Shark think Yuma was the one to hurt his sister, which made Shark hate Yuma and attack him ruthlessly. Yuma tried to make Shark remember the times they Dueled together, how Shark tried protecting his Emperor's Key from Kite, and how much their bond means to him. Yuma also told Shark that his goal is to be Duel Champion and defeating Vetrix and Dr. Faker wasn't worth losing him. To return Shark to normal, Yuma took control of "Number C32: Shark Drake Veiss" and suffered while the "Number" tried to control him. Shark was able to regain his senses and begins to worry for Yuma. When deciding to save Shark or Astral, Yuma couldn't choose and said that Shark is a very important friend to him. To save Yuma, Shark got rid of his remaining Life Points to banish "Shark Drake" and give Yuma the victory. Afterwards, Shark told Yuma how during the Duel that he could hear Yuma's voice and thanked Yuma for saving him. Smiling, Shark then encourages Yuma to win and beat Vetrix, with Yuma promises to carry on his will.

Later, when Shark awakes in the hospital and sees that Yuma's Dueling with Vetrix in the Sphere Field, he begins to worry and rushes over to the Duel Coaster Stadium, calling out Yuma's name as he goes. He then enters Heartland Tower to save Yuma and puts himself in danger in the process, showing how much he cares for him. Shark was even willing to team up with Kite and Orbital 7 to rescue Yuma, despite his hostility towards them. When Yuma challenges Dr. Faker to a Duel, Yuma gave back Shark "Number 32: Shark Drake", asking him to help him, and the latter joins Yuma with a smile. During the Duel, Yuma and Shark supported each other well with their cards, as well as Shark teasing Yuma when he's getting doubts. When the Heartland Tower started to crumble, a piece of concrete was about to hit Yuma before Shark pushes him out of the way to protect him, taking the hit instead.

When the Barian World began to target Yuma for the "Numbers", Shark worried for Yuma's well-being and chases after him when he goes to Duel Fender, even leaving his sister to go after him. When talking to Rio, Yuma learned that Shark often talked about him to her, to his surprise. She told Yuma that she believed it's because of Yuma that her brother hadn't changed and thanked him for being a good influence on Shark. Also, Shark began to spend more time with Yuma as they started to walk home together after school. When Yuma fell towards a cliff ledge, Shark once again put his life in danger to try to save Yuma from falling,. Recuperating in the hospital, Shark was extremely upset how downhearted Yuma was acting and, in his typical gruff fashion, snapped at him. In order to get through to him, Shark swiped the Emperor's Key and lured Yuma into a Duel. With help from Astral, Yuma got his fighting spirit back, much to Shark's happiness. When Astral told Yuma what Shark's true purpose was, Shark denied it, but Yuma was greatly touched. Trying to show his gratitude, Yuma tried to give Shark a hug, only to be pushed away by him.

After Shark came to accepting his fate as a Barian, he was emotionally shattered at the thought of becoming Yuma's enemy and distraught of breaking his bond and friendship with him. Nevertheless, Shark severed his friendship with Yuma and claimed that it was their fate to become enemies. However, Yuma didn't see him as an enemy, but he was willing to fight him to restore their bonds of friendship. As of the final episode, his friendship with Yuma is once more reformed. Shark, Rio, the former Barian Emperors, Kite and the Vetrix family allied with Yuma again to prevent an upcoming disaster in the Astral World.

Astral
At first, Shark had no knowledge of Astral, but Astral has respect for Shark's Dueling skills and the impact he has on Yuma. . If Shark becomes possessed by a "Number" card, Astral and Yuma usually come into conflict with Shark and try to save him from the card's dark influence.

Sometime between Shark and Yuma becoming friends and the World Duel Carnival, Shark's learned of Astral's existence and knows how important he is to Yuma. Knowing Shark is trustworthy and strong-willed, Astral has no problems letting him keep "Number 32: Shark Drake" card in his possession. After the Duel with Vector, Shark can now see and hear Astral, but they still have little contact with each other.

Once Astral's theories about Shark and Rio being Nash and Marin were confirmed true, he readily accepted that Shark was his enemy when he saw him with the Barians. Despite beings enemies now, he showed concern for Astral when he attempts to sacrifice himself.

Kite Tenjo
Having heard about the "Number Hunter", Shark already knew Kite's reputation, but officially met him when he stopped Orbital 7 from killing him and demanded that Shark hands over the Emperor's Key. Shark figured out that Kite was the "Number Hunter" and his intentions towards Yuma, then lied about having a "Number" card. This resulted to a Duel between them, where Kite easily defeated Shark, taking the key and the latter's soul. Shark bared a grudge against Kite since then, and meeting again in Heartland Tower, he was very hostile to Kite, though he did help free him from the rubble that had trapped him. However, Kite didn't care about it as his little brother, Hart, was in trouble and told Shark they could have a rematch later. After arguing, the two agreed to work together to save Yuma and Hart.

During the Duel with Dr. Faker, they developed a friendship and worked well with each other. Although Shark holds little contact with Kite, they come together if the Barian World poses a big enough threat, but they have a tendency to argue with one other. Initially, Kite refereed to Shark by his first name, but as they were around each other more often, he began using Shark's nickname just as others do.

Though despite their differences, both he and Kite are a lot alike, both do whatever they can to protect their siblings (Hart and Rio) and become quite vengeful and angry with both are in danger, as well as both seem to posses cool and distant personalities.

After Shark had sided with the Barians as Nash, Kite readily accepted that he was now his enemy and was resolved to fight him if he had to.

Quattro
Shark's earliest acquaintance with Quattro was at the National Duel Circuit, where he was Shark's opponent in the final match, which he won by disqualification. He becomes Shark's target of revenge when he revealed that he set Shark up for disqualification by placing his Deck so that Shark could see it, and was the one responsible for Rio's injuries. Shark entered the World Duel Carnival in order to get revenge on Quattro, spending most of the time pursuing him. When they do meet, Quattro takes pleasure out of mocking Shark and provoking him, as it was part of the his family's plans to use Shark and make his hatred grow.

However, Quattro developed jealously towards Shark once he found out that Vetrix wanted Shark to defeat Dr. Faker instead of him. At the WDC party, Quattro confronted Shark out of anger, only to grow more irritated when Shark mocked him before leaving. In the finals, they continued to provoke one another as Quattro led Shark to the "Magma Field" field for their rematch Duel. Out of frustration, Quattro brutally Dueled against Shark to show his father that he was better than him. After Quattro lost to Shark, he apologized for his misdeeds and entrusted Shark with the task of defeating Vetrix, which only annoyed Shark. His revenge and anger then shifts to Vetrix, as he was the one who orchestrated the whole thing.

Shark later reunited with Quattro when he came to help him with Duel against Chironex and teamed up him. The two rivals developed a level of camaraderie, although they often traded insults to each other, which made Trey commented that it was hard to figure out if they were on good or bad terms. When Shark sided with the Barians as Nash and broke his bonds with humanity, Quattro was determined to Duel against the only person he called a friend in order restore the bonds Nash once had. After Nash showed how Quattro's allies perished in their Duels with the Barians, Quattro was disgusted at how far Nash had fallen and accepted that he was no longer Reginald. Although Quattro tried one last time to get "Reginald", back he was unsuccessful, and as his soul headed to the Barian World, the rivals bid a sad farewell to each other, with Nash promising to join Quattro in Hell after the war concluded.

Dumon
During his tenure as Emperor of the United Lands of the Poseidon Ocean, he had befriended a knight from another kingdom. This knight, Dumon, had become close with Nash, swearing to defend and fight alongside him and his enemies.

Their friendship even continued on to their next lives, when the two men had been reincarnated as Barians where Dumon would continue to serve Nash once again. Even after Nash had supposedly disappeared from the Barian world, Dumon (now leader of the other Barians) held on to the hope their leader would return one day. Once Vector had mentioned the possibility of their lost leader being on Earth, Dumon became absolutely determined to find and bring his leader back.

Once it became apparent that Nash was indeed the human Shark, Dumon was able to convince him it was his destiny to join the Barians, and finally Nash had joined up with him once again.

Vector
Shark and Vector are arguably arch-enemies; having a mutual hatred spanning far back into the ancient past. In their past lives, Vector was the Prince of the nation that invaded the United Lands of the Poseidon Ocean, which was ruled by Shark's past life– Nash. This made Vector personally responsible for slaughtering Nash's Kingdom using his monster army. On a more personal level, Vector's invasion forced Nash's sister Marin to sacrifice herself to summon the Ocean God Crystalzero, which was a source of enormous grief for Nash. When the two were eventually revived as Barians, their true memories were sealed away by Don Thousand, so the duo did not recognize one another right away. However, their mutual hatred permitted even into their new identities, Nash disliking Vector for his constant defiance. Vector eventually went so far as to establish a "Point system" for every time Nash annoyed him (and absolutely everything Nash said or did annoyed him), finally deciding to betray his leader at 100,000,000 points. .

Following his obtaining of "Number 73: Abyss Splash" and the recovery of his memories, Shark eventually returned to the Barian side as Nash. At that point, he was well aware of his and Vector's previous relationship and menaces Vector from the start. Nash's distrust of Vector and his involvement with Don Thousand proved fortuitous when Vector eventually betrayed his leadership.

Nash eventually fought Vector one final time in revenge for Vector's murder of the other Barian Emperors, especially Marin. Having witnessed many of his atrocities, he believed Vector to be soulless. However during his Duel against Yuma and Astral, Nash referred to the fallen Emperors, including Vector, as the friends he could not save. He also used Vector's "Number C10X" and even refused to detach the Xyz Material that was linked to Vector's soul, suggesting Nash saw him in a new light after his self-sacrifice.

Decks
Shark plays a Xyz WATER Deck consisting of monstrous looking sea creatures such as various races of sharks. He utilizes a Burn strategy in order to quickly gain the advantage through cards such as "Submersible Carrier Aero Shark" and "Explosive Urchin", with a focus on using Level 3 monsters, such as "Big Jaws" to Xyz Summon Rank 3 Xyz Monsters.

Shark uses cards that can counter "Numbers", whether that be negating their effects with "Black Ray Lancer" or taking control of them with "Splash Capture". As his Xyz Monsters are Rank 3, their ATK tends to be on the lower side. He includes cards to decrease the ATK of his opponent's monsters such as "Needle Sunfish" and "Friller Rabca" to make up for this. A cautious Duelist, he includes many cards to counter Spells and Traps, such as "Sea King's Verdict", "Mystical Space Typhoon", "Plate Salvage" and "Skull Kraken".

After acquiring "Number C32: Shark Drake Veiss", Shark's Deck shifted to include more Level 4 monsters in order to Summon "Number 32: Shark Drake" and became more focused on the "Shark" archetype. Similarly, after acquiring "Number 94: Crystalzero" and "Number 73: Abyss Splash", his Deck shifted to include more Level 5 monsters.

Even after learning he was Nash, Shark still uses the same Deck he used before, with the addition of his own "Over-Hundred Number", "Number 101: Silent Honor ARK" and its upgraded form. He has access to multiple "Rank-Up-Magic" cards as well and still includes Level 5 monsters in order to use "Number 73: Abyss Splash". In his final Duel, he utilizes the "Chaos Over-Hundred Number" cards and numerous "Chaos" support cards to call forth "CXyz Barian Hope".