Declan Akaba

Declan Akaba, known as Reiji Akaba in the Japanese version, is one of the main characters and the second CEO of the huge Leo Corporation in the Yu-Gi-Oh! ARC-V anime. Described as a Super Elite Duelist with a genius brain, Declan is the youngest Duelist in history to be certified to Duel in the professional circuit, having done so at age 15.

Declan functions as Yuya Sakaki's primary rival, despite their current alliance, at first due to his capability to Pendulum Summon, and later due to his methods. Despite his early introduction into the series, Declan's name was not mentioned on-screen until episode 8. He the founder of the Lancers, an organization to fight against invaders from other dimensions.

Appearance
Declan is a thin young man with pale skin and grey hair, the front layer being a lighter grey than the back. His hair is arranged in a simple style, flicking upwards at the ends. Declan's eyes are purple, and he wears red-framed spectacles. His ears are both pierced with black stud earrings. Despite his status as the CEO of the Leo Corporation, Declan dresses rather casually, wearing a dark-blue sweater, white pants that end just above his ankles, and white shoes (apparently without any socks beneath them), along with a long red scarf wrapped around his shoulders with the ends trailing to the small of his back. When he was monitoring the You Show Duel School in person, he concealed his identity beneath a large-hooded sweatshirt.

Personality
In general, Declan has a grim and serious demeanor, but he takes an interest in Yuya Sakaki. He is utterly polite without fail, save rare moments of a loss in composure. Unlike other rivals from the previous series Declan is calm and collected, and is shown to be extremely level-headed. Despite his advanced skills, he doesn't seem to be overly arrogant, and is actually quite respectful to Yuya's father Yusho Sakaki, fiercely defending him when he was insulted in a rare moment of emotion. While he does not consider empathy as beneficial on the battlefield, he does seem to enjoy himself while Dueling, and even requested Yuya to demonstrate Yusho's Dueltaining. He was shown to smile when Yuya exerted his full strength. He later admits that while Yuya's feelings gave birth to a great power, this is not always the case and emotions can still cost one on the battlefield.

Despite his declared rivalry with Yuya Sakaki, he does not show any open dislike for him, and in fact defended him from false accusations of attacking Leo Corporation employees; this demonstrates that he may hold a degree of respect for Yuya. Declan has also mentioned that he does not care very much for his father, Leo Akaba, and he demonstrates an intense dislike of his father's ambitions, given the suffering that they have caused. Declan is also pragmatic without regard for the actions of potential allies, offering an alliance with Shay and Selena despite their attacks on his students.

He is shown to be highly analytical and a skilled strategist, and claims he only plays games that he knows that he can win. He used the Maiami Championship as a test to recruit Lancers, and came up with a plan to fend off the Fusion Dimension invasion within only a day. He can show a less moral side when executing his plans, as he had no problem allowing many Duelists to be sealed in cards during the Battle Royal and only cared about the ones that did survive. During his second Duel with Yuya he showed a cruel indifference and revealed that he considers feelings to be a weakness and a tool to manipulate others, as seen when he used Yuya's feelings towards Zuzu to push him to Duel more efficiently by lying about Zuzu's fate after her disappearance. Despite his cold nature, he seems to care closely about his younger brother Reira and gets along with his mother.

In his youth, Declan was more reckless, crossing dimensions (though unaware that he had done so at the time) to find his father after he had disappeared and exposing his hiding place to save Selena. He also spoke far more brashly (in Japanese, he referred to himself as "boku" in contrast with his current self who refers to himself as "watashi", which is the polite form), demanding answers from his father.

Etymology
His character's last name,  Akaba, means "Red Horse". his surname is similar to Seto Kaiba ( Kaiba Seto) from the original/first Yu-Gi-Oh! anime, whose name also has also has 馬 (Uma, Horse), making his character the ARC-V counterpart to him as the similarities of the last names and appearance they share. While his Japanese name Reiji means "Zero Child".

History
Three years before the Maiami Championship, Declan appeared inside Duel Academy via a strange teleportation device. He wandered the halls until he noticed Selena being chased by faculty members. When they cornered her, he watched from atop a wall behind her as she Dueled against them, and was surprised to see that their holograms had mass without an Action Field. He jumped in, Summoning "D/D Cerberus" to defend her. He then offered her his hand, which she took, and pulled her up over the wall. They fled to the harbor, where they were caught by Leo Akaba and several Obelisk Force members, to Declan's surprise. Selena mentioned that Leo wanted to destroy the Xyz and Synchro Dimensions, mentioning that the attack on the Xyz Dimension was about to start, prompting a confused Declan to protest that Leo had not mentioned anything to him or his mother. The Obelisk Force squad then took Selena away, and then one of them placed a miniature teleportation device on Declan's wrist, which sent him back to the Standard Dimension and then self-destructed.

Pre-Maiami Championship
After Yuya Sakaki defeated The Sledgehammer using the Pendulum Summon mechanic, Declan was briefed on the Summon and on Yuya himself by Nakajima. Intrigued by the Pendulum Summon, Declan asked Silvio to learn what he could about Pendulum Summoning, no matter how small the detail and to acquire them, if possible. Silvio successfully acquired the cards, but wanted to use them to Duel Yuya. As Nakajima protested from where he was watching the Duel, Declan arrived and assured him that it was all right. He advised Silvio on the use of Yuya's Pendulum Monsters from behind the scenes throughout the Duel. After Silvio's loss, Nakajima stated that they would need to use other means to seize the cards immediately, but Declan again reassured him that it was all right for now. He looked at a video feed of Yuya, thanking him for putting on a show and murmured Yuya's name.

A week after the first Pendulum Summon, his mother Henrietta arrived back from a business trip. Declan wasted little time in informing her about Pendulum Summoning and Yuya Sakaki, and stated that they'd almost achieved a complete understanding of the Summon. He also informed her of Silvio's supposed attack at Yuya's hands. Declan admitted to being worried that, despite the feat he had performed, Yuya only had a 50% win-loss-ratio, and he was the son of Yusho Sakaki, who had disappeared three years previously and possibly allied with enemies of Leo Institute of Dueling. Later, he observed the Duels between the You Show Duel School and LID, remaining hidden and concealing his identity beneath a hooded sweatshirt. After Yuya had defeated Dipper, Zuzu Boyle had been defeated by Masumi Kotsu and Gong had tied with Yaiba Todo, Henrietta angrily proposed a tiebreaker between the students that had won; Yuya and Masumi. Before the situation could progress any further, Declan revealed himself and he stated he would put an end to it.

None of the students present recognized Declan, his mother commenting that they didn't know how strong he was. Declan requested that she and their students stay quiet and watch, and that they not cheer any further. Declan allowed Yuya to choose whichever Action Field he wanted, so Skip Boyle (the only You Show member aware of Declan's identity) picked Yuya's favorite Field, "Athletic Circus." In exchange, Yuya let Declan go first. Declan proceeded to use three "Covenant" Continuous Spell Cards to Fusion Summon "D/D/D Blaze Overlord Temujin" on his turn (this is his first use of a Fusion Monster to be known, and there were no record of him using them during any of his past Duels), then set the rest of his hand, but leaving him apparently guaranteed to take 3000 damage on his next turn. When Yuya attempted to retaliate, Declan activated another "Covenant" card that would cause him to take another 1000 damage during the next turn. Yuya was able to counter that attack as well, but Declan was well-prepared, using an Action Card to protect "Temujin." Yuya was given the option to end his turn and theoretically win, but hesitated. Declan observed that Yuya's kindness was causing him to hesitate, though he called it useless in battle. Yuya Set a card, then Declan negated and destroyed his "Covenant" cards with "Lease Laundering," replenishing his hand in addition. Yuya admitted that he wouldn't have been happy if he'd won from that, as he wouldn't have gotten a chance to show off his father's Entertainment Dueling. Declan asked if he was referring to Yusho Sakaki, and Yuya was surprised that Declan seemed to know his father. Yaiba mocked Yusho from the sidelines, prompting Declan to roar at him to be silent. He apologized for his outburst, explaining that he respected Yusho from the bottom of his heart. Declan then proceeded to Synchro Summon "D/D/D Gale Overlord Alexander" and Xyz Summon "D/D/D Wave Overlord Caesar" on his next turn, much to the shock of the onlookers. He destroyed all of Yuya's monsters, despite Yuya's use of "Hippo Carnival." Yuya proceeded to Pendulum Summon on his next turn, using his "Odd-Eyes Pendulum Dragon" in combination with "Performapal Fire Mufflerlion" and an Action Card to destroy all three of Declan's monsters. Declan used the effect of "Caesar" to revive them, though at the cost of taking damage again on his next turn, and then he Tributed them with "D/D/D Resource Management" - bypassing the damage he would have taken - to add his "D/D Magical Astronomer Galilei" and "D/D Magical Astronomer Kepler" to his hand - Pendulum Monster prototypes that he proceeded to activate on his next turn. He congratulated Yuya after Yuya claimed that he looked forward to seeing whatever surprises Declan had in store, Declan asking Yuya to confirm whether Pendulum Summoning was unique with his own eyes. Declan then Pendulum Summoned three "D/D/D Hell Armageddon the Cruel End Overlord", destroying all of Yuya's monsters again and reducing him to 350 Life Points, also discovering, to his surprise, that destroyed Pendulum Monsters were sent to the Extra Deck instead of the Graveyard. Yuya demanded to know where Declan had acquired Pendulum Summoning, but Declan refused to answer. Yuya Pendulum Summoned his destroyed monsters back, along with a new one, "Performapal Partnaga," and attempted to destroy all three "Hell Armageddons", but the destruction of one simply activated the effects of the others, which gained the ATK of the destroyed "Hell Armageddon." Before Declan could counterattack, his Pendulum Monsters' effects appeared and reduced their Scales, destroying his remaining "Hell Armageddons." He burst out laughing in surprise, realizing that Pendulum Summoning was not complete and that he had seen the possibility for further evolution in Pendulum Summoning. His mother then called out his name after hearing about the disappearance of Marco and Nakajima briefed Declan on what had happened. Declan gave Yuya the win, and when asked, told Yuya his name before departing. Arriving back at LID, he learned that Marco had been involved in a Duel with an Xyz user. As they'd been with Yuya at the time, and Yuya had not demonstrated the capability, this ruled him out as the culprit. Declan ordered his men to search for Marco after being shown Marco's cards and Duel Disk.

Following this, Declan anonymously requested that Yuya be allowed into the Junior Youth Championship. Yuya, however, declined, and won his first Duel of the required four to gain entry normally. Nakajima later informed Declan of this, and Declan smiled, commenting that it seemed he'd done something unnecessary, that he should have expected it of the originator of Pendulum Summoning, and he asked if Yuya had Pendulum Summoned and if there was any change. Nakajima replied that there wasn't and admitted that he was bothered by elevated levels of Fusion Summoning that were occurring. The readings were stronger than normal, and Declan compared it to the abnormally strong Xyz Summonings that had occurred recently. He ordered it to be monitored. His mother later approached him with two cards that had been sent anonymously to LID that morning depicting Marco and Tio, one of LID's aces. Declan mused that the previous day, another strong Xyz Summon had been detected, and deduced that the two had been sealed inside the cards, though this was the first time he'd witnessed such a phenomenon. Though Marco and Tio were alive, they couldn't be saved with LID's current resources. He commented that this did raise one question - there had been there Xyz-related attacks, yet the first victim - Silvio - hadn't been sealed in a card, suggesting two perpetrators. Before they could continue their talk, Mr. Sawatari barged into the office furiously, asking why they were loafing around. Despite Mr. Sawatari not having an appointment, Declan acknowledged that the rumors of the third attack were true. Mr. Sawatari angrily asked why they weren't taking action to catch the perpetrator, pointing out that his son had testified that Yuya Sakaki had attacked him. Declan asked if Silvio was still saying that, and Mr. Sawatari admitted that he hadn't seen Silvio since he'd left the hospital, but hadn't heard Silvio say differently. He asked why they were letting Yuya run free, despite Henrietta wanting to handle it herself, and wanted to inform the police. Rising from his chair, Declan warned him that it was under investigation. Mr. Sawatari insisted that Yuya was the perpetrator, but Declan forcefully told Mr. Sawatari that Yuya was no criminal. He vowed to catch the real criminal, until then, he'd like Mr. Sawatari to watch quietly. After Mr. Sawatari had left the office in a huff, Declan ordered Nakajima to raise the level of alert in the inner city and analyze the cards of Marco and Tio to save all of the city's Duelists. He later learned that the strong Fusion Summoning readings were continuing, and mused that the person using them must be winning as well.

Later, Declan practiced Pendulum Summoning again, this time with the effects of his cards updated, and he successfully Summoned all three "Hell Armageddons." Imagining himself facing Yuya and "Odd-Eyes Pendulum Dragon", Declan reached for his next card, but before he could continue his move, he was advised to stop, as they had cleared the day's benchmarks and the experiment was a success. Nakajima congratulated him, stating that now they were one step closer to creating even more of the Leo Corporation's own Pendulum Cards. Despite this, Declan considered his own inferior in terms of activation energy output to Yuya's Pendulum Monsters, believing them to be incomplete and unusable in the tournament. He gave Nakajima until the tournament to fix the problem, as they could not underestimate their competition, no matter where it came from.

When Nakajima was complaining about using students to draw out the Duelist that had been attacking their students, Declan arrived and ordered them to continue monitoring them, confident that whoever it was would show themselves. He witnessed Shay admit to attacking the LID students and the start of his Battle Royale against Masumi, Yaiba and Dipper. When Shay defeated all three of the students and he ordered the other LID students that had arrived to bring them their boss, Declan replied that he was right there if Shay wanted him, and his employees parted as Declan walked towards the Xyz-user. Declan explained to Shay that he was the current Leo Corporation President, and Shay immediately challenged him to a Duel. Declan requested to know why Shay was attacking them. Though Shay refused to answer, Declan had deduced from his actions and Masumi's prior testimony that Shay was trying to rescue his comrades by using Declan as a hostage. Shay confirmed that his attacks had been to lure Declan out to persuade Leo Akaba to release his comrades. Declan claimed that he doubted his father valued him that much, but agreed to Duel Shay under conditions: Shay must enter the Junior Youth Championship and fight certain Duelists for him, informing him in a roundabout manner of Sora Shiun'in, a Fusion user, and Yuya, the user of the Pendulum Summoning that Shay would likely be unfamiliar with. Declan explained that he too wanted to fight against his father and clarified that if Shay won, he could do whatever he wanted. He departed with his men afterwards. Nakajima later confirmed that Yuya had successfully entered into the competition and that Shay had been wiped from Masumi, Dipper and Yaiba's memories, and entered into the Junior Youth tournament. Declan mused that all that was left was to see how much power Shay would display, and he looked through his Lancers Selection document, muttering that the same question applied to the rest of the Duelists in the folder - which of them would become the lances to fight for their world?

Round 1
At the beginning of the tournament, Declan made one of his first public appearances in a while, much to the delight of his fans. He, his mother, and Reira watched the opening proceedings, observing the entry of both Yuya and Shay, and after Yuya's brief mess-up and subsequent speech regarding Yusho Sakaki, Declan led the applause. He watched Reira's first Duel against Ally, and congratulated his little brother after he won.

Before Silvio's Duel with Yuya, Declan gave him his new "Yosenju" cards, including some Pendulum Monsters, and taught him an anti-Pendulum combination that would return Pendulum Cards to the Deck. He monitored the Summoning, which was successful, as was Silvio's use of the technique. He was pleasantly surprised when Yuya Fusion Summoned using a Pendulum Monster as the Material, pleased that Yuya had already evolved so far. After Silvio's lost, he ordered Nakajima to retrieve his Pendulum Cards and analyze them for mass-production.

Before Shay's Duel with Sora Shiun'in, Declan arranged for the Action Field "Future Metropolis Heartland" to be used to light Shay's fighting spirit. Declan also had a Pendulum Card made for Shay, who rejected it. While this annoyed Nakajima, Declan was fine with the rejection of his gift, as he was more interested in Shay's abilities rather than the potential of Pendulum Summoning. He was quite surprised when Shay performed a Rank-Up-Xyz Evolution during the Duel. When Shay called out "Raidraptor - Revolution Falcon," he told Reira to watch their future at stake. After Shay defeated Sora, he told him not to take further action in the eyes of the public, as Sora would be useful for experiments to understand Duel Academy.

Sora escaped during the night, and Declan coordinated the search for him, finding him in Central Park with a man who resembled Yuya Sakaki. Shay explained that this was his comrade, Yuto, the second Xyz user that Declan had suspected of attacking LID. He refused to let Shay assist Yuto, and they simply watched the Duel between Sora and Yuto, and the subsequent arrival and joining of Yuya. After Sora revealed himself as an agent of Duel Academy, his Duel Disk transported him away. Declan watched as Yuto explained to Yuya about the four Dimensions, growing angrier as he heard about the attacks on Yuto's homeland, and explaining that it was due to his father, Leo Akaba's ambition that the tragedy had occurred. Before he could learn more, the security camera they were accessing was damaged. Declan still refused to let Shay go, warning him that he would protect his city in his own way. When they detected a Synchro Summoning reaction, Shay explained that Yuto must be Dueling the Pawn of Fusion. Nakajima later found Yuto's Duel Disk, and Declan ordered it brought to him as he looked out over Maiami City. Nakajima did as ordered, and Declan proceeded to scan it for information.

Round 2
Declan witnessed Yuya's next Duel with Isao Kachidoki, suspecting that Yuya had possession of Yuto's "Dark Rebellion Xyz Dragon"; his suspicions were confirmed when Yuya Xyz Summoned it. When a stunned Shay turned to go and find Yuya, Declan reminded him of the tournament's purpose before he left. Declan then heard Nico Smiley announce that Dipper had lost his Duel to Michio Mokota by default due to absence. This confused Declan, until he was informed that a Fusion Summoning reaction had been detected. He was shown security camera footage that caught Dipper being sealed inside a card by Selena, whose face he recognized. He then learned that Selena had watched Yuu Sakuragi's Duel and realized that Yuu would be Selena's next target, so he devised a plot to use Yuu as bait to lure Selena, which worked perfectly. Declan immediately told Yuu to leave, and as the latter turned to do so, Selena chased him, until Declan stopped her by grabbing her arm. This prompted Selena to threaten to take Declan out first, until Barrett, Selena's cohort, challenged Declan instead. Declan prepared his Duel Disk, ordering Nakajima through a communication link to seal off the area. Declan inferred from Barrett's use of Medal Counters and willingness to take risks that Barrett had extensive combat experience, which Barrett confirmed. Though Declan eventually took damage from his own "Covenant with the Swamp King" card, earning a respectful comment from Barrett, this damage ultimately sealed Declan's victory, as he proceeded to dispatch Barrett using "D/D/D Sniping Overlord Tell" and "D/D/D Oracle Overlord D'Arc". Selena turned to leave, until Declan told her to wait.

He commented that she wasn't Zuzu Boyle, and Selena asked who Zuzu was. Declan explained that Zuzu was someone from Standard that resembled Selena and introduced himself, asking her if she remembered him and if she had been sent by Leo Akaba as a vanguard for an invasion. Selena denied working with Leo, having come to Standard of her own free will, and she admitted that she remembered Declan too, as she'd been trapped in that castle since Declan's appearance in her world. Declan explained that he was opposing Leo and offered an alliance, but Selena refused, explaining that she was after the Xyz users in Standard under the belief that defeating them would make Leo Akaba acknowledge her abilities. She gave Declan the card containing Dipper's soul, and Declan informed her that neither Dipper nor Yuu were her target, though he claimed to not know the Duelist from the Xyz Dimension who had defeated Sora. Declan warned Selena that he would be considering her an enemy even if she wasn't working with Leo and would take appropriate action. Barrett, overhearing this, activated the forced return function of his Duel Disk, returning to the Fusion Dimension, but alerting them to Selena's location. Selena explained that there would be people from Duel Academy coming after her, which would cause more than just a disturbance, but claimed before departing that once she'd defeated them and the Duelist from the Xyz Dimension, Leo would have no choice but to acknowledge her abilities.

Battle Royal
To prepare for the impending invasion, Declan organized the third round of the Championship as a Battle Royal between the 16 remaining competitors, as he was worried that simply warning the citizens would cause a panic. He intended for the Top 8 Duelists from the Youth Championship to intercept the invaders, and for the Junior Youth Duelists to take them out. He instructed Shay to monitor the Junior Youth Duelists and seek out those who could join the Lancers in case of an emergency, to which Shay argued that he'd have to abandon those orders if the Youth Duelists all got defeated. Declan later returned to his control room to monitor the proceedings. He cut the video feed from the Ancient Ruins Area of the Action Field to the stadium when Obelisk Force appeared, followed by the Volcano Area when Selena showed up, then ordered the Youth Duelists to move out. He took note of a powerful Synchro Summoning reading in the iceberg area, theorizing that it was the Pawn of Fusion that Shay had spoken of. When the Obelisk Force appeared before Selena, he ordered the Youth Team to be sent to the Volcano Area. The Obelisk Force whittled down the Youth Team until only Yuu remained, though he was saved by a Duelist from the Synchro Dimension who wiped out the entire Obelisk Force. Declan realized from this that the Synchro Dimension wasn't their enemy and that LID weren't skilled enough to resist Duel Academy. He theorized that the Duelists from Yuya's generation might be able to become stronger due to entering the new stage of Dueling that Pendulum Summoning had brought about. Silvio then barged into the control room, demanding to know what was going on. Declan decided to send Silvio into the Battle Royal to provide assistance, filling him in on the situation (though apparently, not of the intrusion penalty for the Battle Royal.) He also witnessed the transportation of Zuzu and the Duelist from the Synchro Dimension. After the timer for the Battle Royal expired, Declan met the survivors personally, telling them that he had seen all of their Duels.

Different Dimensions
He revealed that he had changed the third round of the tournament to a city-wide Battle Royal to drive the Obelisk Force away with their abilities. Since they had managed to win and survive, he stated that they should be proud of their triumph over such a strong enemy, but Yuya instead blamed him for Zuzu, Michio, Teppei, and everyone else who had been sealed into cards. Yuya then tried to punch Declan, but Declan easily caught and repelled the attack, saying that Yuya should express his anger with a Duel, not with his fists, and that if Yuya won, he would repent his actions until Yuya was satisfied. He explained that he was determined to rally the Lancers to protect their world from the same tragedy that befell the Xyz Dimension, while activating "Future Metropolis Heartland". Declan requested that Shay explain what had happened to the Xyz Dimension, but Shay was unable to do so out of shame. Declan began to explain it himself, but was interrupted by Yuya (and Yuto who was still inside Yuya) angrily commanding him to stop talking and start Dueling. During the first turn, Declan managed to Summon the same Fusion, Synchro and Xyz Monsters he Summoned during his last Duel against Yuya. After Yuya Summoned "Rune-Eyes Pendulum Dragon" and "Beast-Eyes Pendulum Dragon", Declan hypothesized that Yuya's ability to Fusion Summon was due to Sora's strength affecting Zuzu, and in turn Yuya, though he reassured Yuya that it was merely a hypothesis. After managing to survive Yuya's attack, Declan told Yuya that he understood how Yuya felt about Zuzu, concluding that it was those feelings that enabled Yuya to Pendulum-Fusion Summon, but growing through feelings alone wouldn't be enough to defeat Duel Academy. When Yuya protested that he didn't want to become a Lancer, Declan asked if that meant he didn't want to save Zuzu, which prompted Yuya to believe that Zuzu hadn't been sealed into a card. Declan then told Yuya to defeat him if he wanted to save Zuzu and defeat the Academy. Declan Pendulum Summoned on his next turn, bringing out "Oblivion King Abyss Ragnarok", using it to revive "Caesar" and banish "Rune-Eyes". He then fused his two "D/D/D" monsters into "D/D/D Caesar Ragnarok the Wave Complete Oblivion Overlord" and destroyed "Beast-Eyes". He urged Yuya to show him his full strength, as he hadn't gone all out either. Yuya proceeded to Pendulum-Xyz Summon on his next turn, bringing out "Dark Rebellion Xyz Dragon" and nearly defeated Declan, but Declan was able to survive with the effect of "Caesar Ragnarok." He brought out "Hell Armageddon" on his next turn, along with "Abyss Ragnarok" from the Extra Deck, and Pendulum-Xyz Summoned himself to call out "D/D/D Kali Yuga the Twin Dawn Overlord" and destroyed "Dark Rebellion". He wondered what bonds Yuya's Pendulum-Xyz Summon had been born from and learned that Yuya was fighting not only to save Zuzu but also to keep a promise to Yuto. Yuya revived "Dark Rebellion" and used his "Xiangke Magician" and "Xiangsheng Magician" to overlay "Dark Rebellion" and "Odd-Eyes" to Xyz Summon "Odd-Eyes Rebellion Dragon". Upon seeing this, Declan smiled, declaring that this was what he wanted to see. Yuya launched a winning attack, thinking that he'd sealed Declan's Set cards, but the immunity of "Kali Yuga" allowed Declan to destroy and re-Set his cards, then use them to have "Kali Yuga" defeat "Odd-Eyes Rebellion Dragon", winning him the Duel. He reminded Yuya that he was naive, but claimed that he still had hopes for him, and all of the Lancers, who he'd chosen to cross dimensions with him. Walking away, he asked Nakajima if he'd collected the data from the Duel, and Nakajima replied that he had.

After Henrietta revealed the existence of the different dimensions, Declan outlined the Lancers to the public, also effectively turning it into a propaganda advertisement for LID, which would train the next generations of Lancers. He provided new clothes for Selena and she stayed under his protection. The next day, Declan gathered the Lancers at the Leo Corporation, informing them that they would be going to the Synchro Dimension to recruit allies in their fight against the Academy and also explained that Reira would be going with them. He explained that he'd used the technology in Yuto's Duel Disk to upgrade those of the Lancers to travel between dimensions and project an Action Field, and Selena forced him to admit that he'd seen Zuzu be transported to the Synchro Dimension. The Lancers then departed.

When the Lancers arrived they were split into several groups. Declan's whereabouts were unknown to most of the Lancers and several of them attempted to find him for days with no success. When Tsukikage rescued Reira from Security Selena suggested that Declan instructed him to do that.

After the Lancers were taken to the Executive Council and Yuya claimed they did not want to cause trouble, Declan appeared with Tsukikage and Reira. He revealed to Jean-Michel Roger that they came to the Synchro Dimension in order to form an alliance. To help reinforce the Lancers' trust with the Synchro Dimension, Declan suggested they take part in the Friendship Cup, which Jean agreed to. He then quietly observed Yuya's Duel against Jack Atlas with Tsukikage, Reira, and the Executive Council. Declan suggested that Reira enter the Friendship Cup and mentioned that he had no problem letting Reira live with the other Duelists.

Reira
While Declan and Reira aren't as close compared to other pairs of brothers in the previous series such as the Kaiba brothers, they still are shown to care about each other. Reira was encouraged by Declan's compliments after his victories during the Maiami Championship and was allowed to join the Lancers despite not being at the Battle Royale. When some of the Lancers complained about Reira joining, Declan quickly defended him and said that he would not be a hinderance.

When the Lancers were split at the Synchro Dimension Reira cared about nothing but finding Declan as soon as possible, and Declan allegedly requested Tsukikage to find Reira.

Leo Akaba
When Declan encountered Leo at the Fusion dimension he was suspicious of his father's ambitions and later founded the Lancers to fight against him. He claimed that Leo doesn't care about him when Shay planned to use Declan as hostage. Declan was furious when he heard about the suffering that his father had caused.

Shay
When Shay and Declan met face to face, rather than dueling Shay, Declan decided to form an alliance with the Xyz Dimension Duelist. However he frequently has to keep Shay under vigilance so his recklessness doesn't affect his plans.

Selena
When Declan arrived at the Fusion dimension and met Selena, he tried to help her escape without hesitation. Despite knowing Selena's alliance to Academy, Declan trusts her and plotted her to join the Lancers knowing she wouldn't betray them. Selena likewise accepted to help Declan combat the Fusion Dimension and supported his plan to go to the Synchro Dimension to recruit allies.

Yuya Sakaki
During their first Duel Declan and Yuya were respectful to one another and Declan revealed that he respected Yuya's father. During their second Duel however, Declan showed indifference towards Yuya's feelings, disregarding them as a weakness even though he acknowledged the strength that they gave him, and instead used them to manipulate him and push him to become stronger. During their Duel, he refused to tell him the truth about Zuzu's disappearance and only told him the truth just as they were about to leave for the Synchro Dimension, where Zuzu was (and even then, likely largely due to Selena figuring this out herself and so Yuya would be more determined to go there).

Deck
Declan uses a "D/D" Deck, which utilizes the "Covenant" archetype of Spell and Trap Cards to easily gather the necessary cards to perform the Fusion, Synchro, Xyz, and Pendulum Summons of the "D/D/D" monsters, using cards such as "Lease Laundering" and "D/D/D Resource Management" to avoid the negative effects of his cards.

Declan's usual strategy involves Fusion Summoning "D/D/D Blaze Overlord Temujin" through "Covenant with the Swamp King" to load his Graveyard with resources to summon more monsters, often using them along "D/D Night Howling" by reutilizing the monsters in his graveyard and subsequently Synchro Summon "D/D/D Gale Overlord Alexander" and use the effects of both "Temujin" and "Alexander" to reutilize the Graveyard in order to Xyz Summon "D/D/D Wave Overlord Caesar", attacking with the 3 monsters in order to perform an OTK against the opponent.

If this strategy fails Declan resorts to other means, often involving his true ace-monster "D/D/D Hell Armageddon the Cruel End Overlord" summoning one or multiple copies of it through Pendulum Summon, sometimes accompanied by "D/D/D Oblivion King Abyss Ragnarok". He can also however utilize the effects of "Caesar" to avoid losing field advantage or simply summon other boss monsters through different means depending on the situation, although he usually prefers Fusion Summon by banishing previously used D/D monsters through "Swamp King", being able to summon "D/D/D Oracle Overlord D'Arc" to counter burn tactics and "D/D/D Caesar Ragnarok the Wave Complete Oblivion Overlord" for nearly unparalleled ATK power. He can also Xyz Summon "D/D/D Sniping Overlord Tell" to utilize the effect damage he receives to punish the opponent or "D/D/D Kali Yuga the Twin Dawn Overlord" to protect his cards and remove his Spell/Trap cards and return them to their previous state instantly, allowing him to use them even if his opponent had activated an effect to prevent him from using them. Declan is capable of using the Pendulum-Fusion and Pendulum-Xyz Summoning techniques to call out his monsters.

Over the course of the Series, some of the cards used by Declan have been changed with regards to their effect or type. This is the list of cards which he used previously.