Ryoga Kamishiro, nicknamed "Shark", is one of the main characters in the Yu-Gi-Oh! ZEXAL manga and is one of Yuma Tsukumo's rivals. According to Kazumo Tsukumo, he is the Duelist who has the soul that governs the oceans of the Astral World.
Shark has dark blue eyes, pale skin and dark purple hair, which resembles tentacles hanging down, referencing his Deck theme of aquatic creatures. His accessories include a grey, shark tooth-shaped pendant, and two grey rings on his right hand. He also owns a grey and green Duel Gazer with a red lens and a yellow spike. He also wears a large red jeweled, yellow pendant that resembles a Barian Emblem. His attire includes a dark purple jacket over a black shirt and dark pants with white, green-gems shoes. When in his school attire, he wears a white shirt with green-lined sleeves, tie and a collar.
Ryoga has been shown to be extremely cruel, shown when he snatched Tetsuo's Deck and then snapped Yuma's pendant just to show Yuma that he was powerless. Despite this, he is shown to keep his word as he gave Yuma Tetsuo's Deck after he was defeated.
Shark is an orphan, and was raised in an institute, together with Kyoji Yagumo. He and Kyoji were like light and shadow there, but they weren't on bad terms. Once, both he and Kyoji entered the Duel Monsters Regional Cup. There, Kyoji wanted to steal the Deck of the person who was most likely to win the tournament, but failed, and Shark took the blame for it.
One day after school, Shark had a Duel with Tetsuo Takeda, which was watched by Yuma Tsukumo and Kotori Mizuki. When Shark defeated Tetsuo, he took his Deck. Tetsuo revealed that Shark and his friends had taunted Tetsuo to the extent that he bet his Deck on the Duel.
Yuma attempted to defend Tetsuo, but Shark took Yuma's pendant and snapped it. He then told Yuma to challenge him to a Duel in front of the Heartland train station in order to win Tetsuo's Deck back, but he must put his Deck on the line. Shark overpowered Yuma during the Duel, but when Yuma decided to believe in himself, his broken pendant restored itself, and Yuma uses it to open the door of his dreams. When he does so, a dark card, called a "Number", possessed Shark, making him even stronger. However, at the same time, a mysterious entity, called Astral appeared before Yuma, and told him to "stand up and win".
Astral then helped Yuma during the Duel, but they find out a "Number" can only be destroyed by another "Number", and when two of them battle, they do to consume each other. Astral gave Yuma a "Number" as well, and they managed to defeat Shark. As Shark gave Tetsuo's Deck back, Yuma said that the Duel was fun, and that they should Duel again. Shark said that he won't forget that, and leaves.
She soon revealed herself as Luna, and said that Shark can call her an emissary from the moon. Shark replied that she looks like something straight out of a fairy-tale, not that he hates them. Luna replied that she doesn't have any ill will against him, but she must face him. They then began a Duel.
The Duel ended quickly, with Shark defeating Luna in an OTK. After he won, Shark asked Luna if she is alright; she is impressed that Shark could Summon three Xyz Monsters at once during the Duel, and said that she wasn't wrong. Luna revealed she is a Numbers Hunter whose goal is to eliminate the "Numbers", and says that Shark is the only one who can stop Dr. Faker, and for that he needs the power to do so - a "Number". Shark declined, saying that he was already once possessed by a "Number", and that he cannot do so. However, Luna replied that he knows how terrifying a "Number" can be, and that this is just why it would be okay. She further explained that "Numbers" are mirrors that reflect the hearts of the people, and at that time, his heart was full of darkness, but Yuma and Astral freed him from that darkness. She then gave Shark a mysterious card, and said that it's a new power that will protect him
Later, Shark Duels a self-made store owner, whose business was going well because of the power of a "Number" card. Shark won easily using the new "Number" Luna gave him, "No. 47: Nightmare Shark", and obtained the store owner's "No. 63: Shamoji Soldier". Then, Yuma and Astral appear, and meet him. Before they could say anything, Kaito Tenjo appeared as well. Shark recognized Kaito, and Kaito says that as Shark knows his name, he seems to have became rather famous. Luna then appeared, and told Kaito that's because she told Shark the truth. Later, when Kaito tried to use his Photon Hand on Luna, she put her hand over the amulet on her chest, which created a kind of barrier covering her, Shark, Yuma and Astral, and reflecting the Photon Hand. The four are then instantly transported to the outskirts of Heartland City. Yuma and Shark stared at each other for a moment, and Shark told him that he would wipe out his "Numbers" as well one day, as he turned to leave with Luna. 
Following this, Shark speaks with Luna and he thanks her for the "Number" she gave him as it allowed him to see something interesting. Luna mentions now that Kaito has shown up along with Yuma and Astral, all the players are now in place. All except for one Shark adds. Shark says that if what she said is true then he must know the truth as that is the reason he decided to help her destroy the Numbers. Luna responds "Kyoji Yagumo... The one who changed your fate...". As Shark stares at the moon, he thinks to himself that if Kyoji is going to make the wrong move he'll be there to stop it. Shark thinks back to his time at the orphanage and Dueling Kyoji in a tournament as Luna correctly guesses that Shark took the fall for Kyoji when he stole that Deck. Shark grits his teeth as he wonders why Kyoji stole the Deck in the first place as he was the hope of the children in the orphanage. 
When Yuma begins a Duel with Eviluder, Shark and Luna watch from a rooftop. Luna asks Shark if he is going to make a move and Shark replies that now is not the time as he notices Kaito is watching the Duel as well. Shark becomes surprised when he sees the size of Eviluder's "No. 42: Galaxy Tomahawk". 
After the Duel ends with Yuma's victory Kyoji appears and punishes Eviluder for losing. Kyoji notices Shark and admits that its been a long time since they last met. Shark asks what happened to him and Kyoji responds that Shark has gotten rude after he last saw him. After remaining silent for a bit, Kyoji tells Shark that hope and despair are two sides of the same coin and that if one has great hope the deeper the despair they will have. Kyoji tells Shark that he is special to him and one day he will teach him what it means. With those words Kyoji leaves. Shark tells Kyoji to wait but Luna says they must leave as well as they can't afford to do anything foolish right now. 
Shark defeated Shadow and claimed "No. 31: Abel's Doom" at some point. Soon after, he Dueled Kaito for his "Numbers". Shark used "Anchor Whale" to nullify the effects of "Galaxy-Eyes Photon Dragon" and transform the field into a deep-sea field, pushing Kaito into a corner. He continued to gain an edge through destroying "Galaxy-Eyes" and a combo of his "Nightmare Shark" and "Bahamut Shark", but Kaito used "Hyper Galaxy" to bring back his ace and reduce Shark's Life points to 1600. Unfortunately, as Shark still held "Abel's Doom", and Kaito had "No. 13: Cain's Doom", the trap Shadow had set was complete, causing the two "Numbers" to summon themselves, reduce both their Life Points to 1000, and wipe out both players' fields, setting the stage for a double knockout.
Yuma began a Duel to save them, paying 2002 of his Life Points to offer half the amount to each of them as "Cain's Doom" and "Abel's Doom" continued to attack each other. During the Duel, Yuma continuously tried to sacrifice his own life for Kaito and Shark's sake, with both being against it. Their wishes to defeat Shadow created a strong bond between them, causing Astral to shine brightly and give birth to "No. S39: Utopia One", leading Yuma to victory and rescuing Kaito and Shark from a narrow defeat..
Later on, Kyoji set a double Duel between Yuma and Kaito, and between Shark and himself, in order to end the Numbers War. Shark quickly Summoned "Bahamut Shark" and "Number 47: Nightmare Shark", but Kyoji countered him with "No. 23: Lancelot, Ghost Knight of the Underworld", whose effect destroyed both of Shark's monsters. Kyoji then explained to Shark about the effects of "Lancelot", saying that it was easy for him to surpass Shark then. Before going on with his turn, Shark asked Kyoji what caused him to fall that far, with Kyoji agreeing, explaining that he did want Shark to know what happened to him. Joking, Shark said that it should be good, and asking if it was hell; trembling, Kyoji said that yes, it was indeed hell, and explained that his brother died by his own hand. Kyoji then explained to Shark about the history involving him and his brother.
Shocked at what he just heard Shark asks Kyoji again what happened to him. Kyoji responds that he just told him it was hell. Luna calls Shark on his D-Pad and asks him to stop the duel and not to use any more numbers or the device that Kyoji created will activate. Shark admits that she's right about not summoning any numbers to the field, but he refuses to stop the Duel as his pride as a duelist won't allow it. Using a combo of the trap Hidden Fangs of Revenge and the effect of Medusa's Aegis allows Shark to destroy Kyoji's monster.
Shark became a Number Hunter at the behest of Luna, who gave him "No. 47: Nightmare Shark". He would go on to win "No. 63: Shamoji Soldier" from a restaurant owner and "No. 31: Abel's Doom" from Shadow. The latter card was eventually passed to Astral.
During the Duel against E'Rah, Kyoji Yagumo handed Shark a blank "Number", previously "Number 70: Deadly Sin", which was moulded into "No. 37: Hope Woven Dragon Spider Shark" during the same Duel.
After E'Rah's defeat, Astral absorbed all the "Numbers" held by Ryoga.
Ryoga plays a WATER Deck, with a heavy focus on Xyz Summoning using the effects of cards such as "Chain Summon" and "Bahamut Shark", which is his ace monster. When he received "No. 47: Nightmare Shark" from Luna, his strategy starts to focus on bring him out quickly, the majority of the times using the effect of "Bahamut Shark", so that he can allow the latter to attack directly.Some use of "" in your query was not closed by a matching "".
|Kyoji Yagumo||21||Lose (flashback)|
|Number 63's holder||20||Win|
|Kaito Tenjo||29-32||No result|
|Kyoji Yagumo||38-43||No result|
|Kyoji Yagumo/E'Rah||44-51||Win (with Yuma Tsukumo and Kaito Tenjo); Eliminated|
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