Mokuba Kaiba
Mokuba Kaiba (海馬 モクバ) is a character from the Yu-Gi-Oh! manga, originally created by Kazuki Takahashi. Mokuba is the younger brother of Seto Kaiba. Initially, he is portrayed as a spoiled and vindictive child with a mischievous and malevolent streak. A skilled player of Capsule Monster Chess, he frequently resorted to cheating. His negative traits stem partly from the neglect he experiences from his older brother, to whom he desperately seeks to prove his worth. However, as he befriends Yugi Mutou and his companions, and as Seto learns to appreciate him more, Mokuba’s behavior improves.
| Names | Mokuba Kaiba (海馬 モクバ) Mokie (by Seto when they were young) |
| Gender | Male ♂ |
| Race | Human |
| Occupation | Vice President of KaibaCorp. |
| Origin | Yu-Gi-Oh! Chapter 24: Capsule Monster Chess カプセル・モンスター・チェス！ Kapuseru Monsutā Chesu! (July 4, 1997, tankōbon volume) |
| Alignment | Reformed |
| Height | 142 cm (4ft 8in) |
| Weight | 28 kg (62 lbs) (4.40 st) |
| Created By | Kazuo Takahashi (Japanese: 高橋 一雅) |
| Personality Type | ENFP, 6w7 (Enneagram) |
| Voice Actors |  Japanese: Junko Takeuchi (竹内 順子)
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Appearance
Mokuba has tan skin, grayish-purple eyes, and long black hair. In a flashback, he is shown wearing a greenish-blue long-sleeve sweatshirt, black shorts, white socks, and black dress shoes. In the present, his outfit consists of a white and orange-striped open-collared shirt, a red sweatshirt, a light blue bandana around his neck, bluish-green jeans, and black-and-blue sneakers. Occasionally, he pulls up his bandana like a mask and wears a purple hat to disguise himself. During the Battle City arc and much of the series, he wears a green-and-blue striped shirt, a yellow vest, dark blue jeans, and blue sneakers.
In Yu-Gi-Oh! The Dark Side of Dimensions, Mokuba receives a redesign, sporting a white business suit and a shorter haircut.
Personality
At the start of the manga, Mokuba is hostile and attempts to trick Yugi Mutou as revenge for his brother's defeat. Although he specializes in Capsule Monster Chess, he is not as skilled as Seto. His determination to avenge Seto’s humiliation leads him to extreme measures, such as enlisting friends to threaten Yugi with a machine gun, a knife, and a stun gun to force him into a game.
In the Yu-Gi-Oh! Duel Monsters anime, Mokuba is depicted as eternally devoted to Seto, staying by his side and following his commands. He is more naive and good-natured than his manga counterpart and serves as a reminder of Seto’s humanity. While he acknowledges that Seto can be difficult, he sees the good in him and remains fiercely loyal. Over time, he grows to trust Yugi and his friends, even considering their perspectives. In one instance, before ejecting a pair of brothers from the Battle City tournament, he hesitates and wonders if Yugi would have given them another chance, showing his admiration for Yugi’s values.
In the original Japanese manga, Mokuba typically omits honorifics when referring to people—except for his older brother, whom he respectfully calls "nii-sama" (honorable older brother). His deep bond with Seto is evident, as he remains forgiving even after being hypnotized and brainwashed by Noah, whom he later treats like a brother.
Mokuba is portrayed as kind-hearted but somewhat naïve about the world, though he demonstrates intelligence in technology and business. He is aware of KaibaCorp’s stocks and once devised a plan to protect the company’s reputation. While Seto disapproves of his growing friendships with Yugi and his group, Mokuba ultimately succeeds in forming bonds with them.
Unlike Seto, Mokuba rarely duels. In the first anime series, he does not duel at all, only participating in the second series and manga. A recurring theme in the Yu-Gi-Oh! Duel Monsters anime is Mokuba being kidnapped by Kaiba’s enemies, prompting Seto to reveal his softer side by repeatedly rescuing him. Despite their occasional disagreements, Mokuba is the one person Seto consistently and unconditionally cares about.
Biography
Background
At a young age, Mokuba and Seto Kaiba were orphaned. Their mother died during Mokuba’s birth, and their father perished in an accident when Mokuba was three. Their relatives squandered their inheritance and abandoned them at an orphanage. The trauma of these losses shaped Seto’s worldview, leading him to instill in Mokuba the belief that they could never trust anyone.
When Gozaburo Kaiba, the head of Kaiba Corporation, arrived at the orphanage seeking an heir, Seto saw an opportunity. He challenged Gozaburo to a game of chess, wagering that if he won, Gozaburo would adopt both him and Mokuba. At the time, Mokuba was five years old. Seto emerged victorious, though he had resorted to cheating.
As Seto later overthrew Gozaburo and seized control of KaibaCorp, he descended into ruthlessness, neglecting Mokuba in pursuit of power. In response, Mokuba went to great lengths to regain his brother’s affection.
Death-T
Mokuba led a gang of followers his age, using them to orchestrate revenge against Yugi Mutou for defeating Seto in Duel Monsters and inflicting a Penalty Game upon him. Mokuba had an associate known as "Old Man Dentures" rig a Capsule Monster Chess coin machine to ensure his victory. Later, Mokuba and his gang confronted Yugi at the store, seized him, and forced him into a game. To cover their tracks, Mokuba bribed Dentures with a large sum of money.
The gang transported Yugi and the dispenser to their hideout, coercing him into playing Capsule Monster Chess against Mokuba. As Mokuba had planned, Yugi transformed into Yami Yugi for the challenge. The rigged machine dispensed mostly low-level monsters for Yugi while granting Mokuba an advantage with stronger ones. They agreed on brutal stakes—if Mokuba won, he would cut off one of Yugi’s fingers, but if Yugi won, Mokuba would be subjected to a Penalty Game. Yami Yugi turned the match into a Shadow Game, strategically sacrificing his pieces to lure Mokuba’s into a diagonal line. With his final piece, "Torigun," he wiped out Mokuba’s remaining four monsters, securing victory. As his Penalty Game, Mokuba was trapped in an illusion where he believed he was encased inside a giant Capsule Monster Chess capsule. Before being fully engulfed, he ominously warned Yugi that Death-T was coming.
During the construction of Death-T, a deadly theme park designed by Seto Kaiba to eliminate Yugi, Mokuba insisted on personally challenging him in one of the stages. Although Seto initially discouraged him, Mokuba persisted. The brothers even made a bet on which stage Yugi would die in—Mokuba wagered Death-T 4, while Seto bet Death-T 5.
When Kaiba’s chauffeur escorted Yugi and Joey to the Kaiba mansion, Mokuba greeted them in the car, introducing himself as KaibaCorp’s vice president. Though he claimed they would receive VIP treatment at Kaiba’s grand event, he maintained an air of suspicion. At the mansion, Mokuba invited them to a lavish meal, only to reveal it as a twisted game. The meal consisted of childishly indulgent dishes, placed on a rotating turntable. Mokuba lied, claiming there was no poison, and that a hidden treasure was among them. When Joey went first, Mokuba secretly used a hidden switch inside a syrup bottle to ensure Joey received a poisoned dish. Laughing, Mokuba revealed the game as Russian Roulette Dinner, forcing Yugi to continue playing to win the antidote for Jonouchi.
Yugi transformed into Yami Yugi, who quickly deduced Mokuba’s cheating tactics. Destroying the syrup bottle, Yami Yugi manipulated the game so that Mokuba himself consumed the poisoned dish. Defeated, Mokuba handed over the antidote before collapsing, with a butler rushing to his aid.
The next day, Mokuba prepared for his match against Yugi in Death-T 4. Before the battle, he confronted Seto about their wager, realizing that Seto had bet on Death-T 5, meaning he expected Mokuba to lose. When Mokuba expressed his desire to earn Seto’s approval by defeating Yugi, Seto coldly dismissed him, declaring that there was no place for brotherly love in gaming. Until Mokuba understood that, Seto said, he would always be a loser.
Determined to prove his brother wrong, Mokuba stormed off to face Yugi once again.
Mokuba once again rigged the Capsule Monster dispenser in an attempt to secure victory, but he still lost. Unmoved by his brother’s failure, Seto enforced Death-T’s brutal rules and subjected Mokuba to the Experience of Death Penalty Game. However, Yami Yugi intervened, saving Mokuba from the terrifying punishment.
Shocked by Yugi’s act of mercy, Mokuba asked why he would help him. Yugi explained that he only won because of the support of his friends. This revelation caused Mokuba to reflect on his past, recalling how much Seto had changed since their time at the orphanage. He began to wonder whether Yugi might be able to help his brother when they faced each other in the next round.
Grateful for Yugi’s kindness, Mokuba repaid the favor by rescuing Yugi’s friend, Tristan, who had been trapped in the previous stage of Death-T. After Seto’s defeat and his subsequent Mind Crush Penalty Game, Mokuba shared the history of the Kaiba brothers with Yugi and his friends. Yami Yugi reassured Mokuba that Seto would awaken once he had pieced together the shattered fragments of his heart. Determined, Mokuba vowed to wait as long as necessary for his brother’s return.
Duelist Kingdom
Mokuba was initially imprisoned in a high tower on Duelist Kingdom by Pegasus, who used him as bait to lure Seto Kaiba into a Duel. In the Japanese version, Pegasus also sought a key card that Seto had given Mokuba, which granted access to a facility containing confidential documents necessary for taking over KaibaCorp. However, Mokuba managed to escape by tying bedsheets together into a makeshift rope, though it only reached partway down. After a painful fall, he stole a boy’s Deck and Star Chips, leaving the boy disqualified and forced to leave the island.
Yugi and his friends soon found the boy and promised to help. Returning to the scene, they encountered Mokuba, who jumped out of the bushes and challenged Yugi to a Duel. He played only Man-Eating Plant and Krokodilus before his true identity was discovered. Mokuba then revealed his reason for being on Duelist Kingdom—after Yugi defeated Kaiba in a Duel, Seto had disappeared, leaving Mokuba feeling abandoned. He blamed Yugi for his brother’s absence.
Mokuba also exposed a conspiracy involving Pegasus and the Big 5, KaibaCorp’s board of directors. They had struck a deal with Pegasus to take over the company, planning to dispose of Seto and keep Mokuba imprisoned so he couldn’t inherit the title. To restore KaibaCorp’s reputation, Pegasus needed to defeat Yugi in the tournament. Téa deduced that Mokuba had tried to remove Yugi from the competition so Pegasus wouldn't have to Duel him.
Mokuba later attempted to steal Yugi’s Star Chips in a final act of revenge, but Yugi helped him realize the truth—that Seto was searching for a new path as a Duelist and a person, free from the darkness that had once controlled him. Yugi assured Mokuba that his actions wouldn’t save KaibaCorp or his brother. Accepting Yugi as a friend, Mokuba vowed to help protect Seto from Pegasus. However, before they could act, Mokuba was recaptured and taken away.
Determined to free Mokuba, Yugi agreed to Duel for his freedom, facing what appeared to be the ghost of Seto Kaiba. Mokuba, however, immediately knew it wasn’t really his brother. It was later revealed that Seto had secretly implanted a virus into Blue-Eyes White Dragon, proving that he was alive. The so-called ghost was merely the remnants of Kaiba’s dark persona, which Yugi had previously destroyed. Yugi managed to win the Duel and banish the false Kaiba to the Shadow Realm, but despite his victory, Pegasus’ enforcer Kemo took Mokuba away and locked him in a dungeon.
Seto eventually reached Mokuba’s cell, but before he could free him, Pegasus appeared and stole Mokuba’s soul. This forced Kaiba into an unfair Duel against Yugi, with Mokuba’s soul at stake. In a desperate move, Kaiba backed onto the castle’s edge, threatening to fall with his dragons. He implied that without Mokuba, his life had no meaning. (In the dub, Kaiba exploited Yugi’s kindness, knowing he wouldn’t attack and risk harming him, securing victory by default.)
Although Kaiba won, he later lost his soul to Pegasus after Téa won Yugi the right to enter the castle. It was only after Yugi defeated Pegasus that both Seto and Mokuba’s souls were restored. Reunited at last, Mokuba was overjoyed to see his brother again, and the two reaffirmed their unwavering bond, having never given up on each other.
Legendary Heroes
After returning from Duelist Kingdom, Seto and Mokuba went back to KaibaCorp, where Kaiba immediately confronted the Big Five to exact revenge for their betrayal. However, they convinced him that their actions were meant to help, not harm, him. To prove their loyalty, they revealed that they had completed the virtual reality simulator they had been developing. Intrigued, Kaiba decided to test the simulator before firing them, despite Mokuba's strong objections. Once inside, he quickly realized that the Big Five had sabotaged the system when he was captured by Armed Ninja.
Recognizing the trap, Mokuba grabbed Kaiba’s Deck and ran to find help. He enlisted Yugi and his friends, who followed him to Kaiba’s private lab, where they used additional simulator chairs to enter the virtual world. Yugi, Joey, and Mokuba entered while Téa and Tristan stayed behind to stand guard.
Upon arrival, they found themselves in a graveyard, where Mokuba taught Yugi and Joey how to summon monsters. They then met a fairy named Earu, who guided them to an old town. There, Yugi suggested splitting up to search for clues about Kaiba’s whereabouts. An old woman informed Mokuba that she had seen someone transporting a prisoner toward a mountain, but the only way to reach it was by crossing a vast desert.
Attempting to cross, they were caught in a powerful twister and flung back to the town, leaving Mokuba shaken. An elderly man explained that they needed a special monster, Niwatori, to traverse the desert. To obtain it, they had to enter a tournament and defeat the reigning champion, Madame Butterfly. Joey, under the alias "Señor Porky," entered the competition and discovered that Madame Butterfly was actually Mai. Recognizing Joey, Mai decided to help them by stealing the Niwatori card and making a run for it. Using the card, they successfully crossed the desert, fending off a monster along the way.
Reaching the temple beyond the desert, Mokuba, desperate to reunite with his brother, ran ahead. When the others caught up, they discovered a massive maze inside. Hearing a girl scream, Joey rushed to help, but they were ambushed by Labyrinth Tanks. Yugi used Magical Hats to escape, and they soon encountered Earu again, who led them to a princess named Adina—who looked exactly like Mokuba, except female.
They eventually found the exit, only to be blocked by the Gate Guardian. Yugi and Joey fused Red-Eyes Black Dragon and Summoned Skull with Polymerization, enhancing the fusion with Dragon Nails to defeat the guardian. As thanks, Princess Adina brought them to her castle, where she revealed the legend of the Heroes. However, before they could strategize, an army of monsters surrounded the castle. One captured Mokuba—mistaking him for Adina due to his outfit—and took him to the floating castle where Kaiba was held.
Upon reuniting with his brother, Mokuba freed Kaiba and returned his Deck. However, Kaiba disapproved of Mokuba seeking Yugi's help and showed no gratitude to Yugi, Joey, or Mai. Meanwhile, the Big Five summoned the Mythic Dragon without the required sacrifices. Its first target was Mokuba, the only one without a monster to defend him. Seeing this, Joey ordered Red-Eyes Black Dragon to shield Mokuba, sacrificing himself and vanishing from the game. Mai followed soon after, struck down by the dragon.
Yugi urged Kaiba to work together, suggesting he summon Blue-Eyes Ultimate Dragon, but Kaiba stubbornly refused. As the Mythic Dragon prepared to attack him, Mokuba—realizing the attack was meant for his brother—selflessly pushed Kaiba out of harm’s way. Devastated by Mokuba’s sacrifice, Kaiba finally agreed to cooperate with Yugi, and together they defeated the Mythic Dragon.
After the battle, Adina revealed her true form as the Mystical Elf and used her magic to revive Joey, Mai, and Mokuba. With everyone restored, they exited the virtual world, finally free from the Big Five’s trap.
Battle City
During the Battle City tournament, Mokuba serves as the tournament commissioner, enforcing rules and penalties when necessary. While Kaiba focuses on his Duels, Mokuba patrols the city, ensuring fair play.
The first violation he catches involves the Roba brothers—while the eldest, Espa, is Dueling, his younger brothers secretly use binoculars to spy on his opponent’s hand. Mokuba tackles one of the brothers and is about to disqualify Espa when the younger Robas plead with him, explaining that their big brother protects them from bullies by winning Duels. This resonates with Mokuba, reminding him of his own relationship with Kaiba. Though he refrains from disqualifying them, he warns them not to assist Espa for the rest of the match, commenting that "big brother stories get me every time."
Later, Mokuba intervenes when a Duelist tries to take two rare cards from his opponent, violating the tournament rules. The Duelist refuses to back down, but Seto arrives and swiftly puts him in his place for disrespecting Mokuba. Afterward, the brothers leave together.
While roaming the city, Mokuba and Kaiba encounter Yugi and his friends. Kaiba is shocked to see Joey participating in the tournament and is about to leave when Joey challenges him to a Duel. Mokuba advises Joey against it, warning him that even if he's good, he’s not on Kaiba’s level. However, before the Duel can begin, Kaiba’s helicopter arrives, and the brothers depart.
Mokuba later watches Yugi Duel a mind-controlled opponent. After Yugi wins, Mokuba, in his role as commissioner, awards him Slifer the Sky Dragon, though he jokingly tells Yugi not to get used to it. Before leaving, the mind slave—revealed to be controlled by Marik—threatens Yugi’s friends. Concerned, Yugi rushes off, and Seto and Mokuba follow.
After Yugi and Kaiba defeat two Rare Hunters, Mokuba stays behind to help them search for Yugi’s friends. However, he is ambushed by more Rare Hunters and kidnapped. They tie him up and dangle him from a helicopter, taunting Kaiba by making him Duel alongside Yugi in a high-stakes tag-team match against Lumis and Umbra. The losers would plummet to their deaths (or, in the dub, be banished to the Shadow Realm).
While the Duel unfolds, Mokuba is taken to a warehouse and locked up with Téa. The two stack crates to reach an opening, allowing Mokuba to escape. Though he gets away, Téa is recaptured. Mokuba is then ordered to find Yugi and Kaiba. He uses a helicopter to pick them up, and during the flight, he realizes that Yugi has two identities. However, Kaiba dismisses it as nonsense and tells him not to pay attention.
They soon learn that Joey has been brainwashed, forcing Yugi to Duel him to break Marik’s control. As the Duel unfolds, both Yugi and Joey narrowly escape death. Relieved that everyone is safe, Mokuba leaves with Kaiba to prepare for the tournament finals.
When the finalists arrive to board Kaiba’s airship, security initially blocks Yugi and Joey’s friends, stating that only Duelists with official IDs are allowed on board. However, Mokuba overrules them, telling Roland to let them on, pointing out that he himself doesn’t have an ID, and Kaiba doesn’t mind either. Throughout the finals, Mokuba watches the Duels alongside his brother and even attempts to decipher The Winged Dragon of Ra’s mysterious text.
Virtual World
During the Virtual World arc, Mokuba and Seto are taunted by Noah, who forces them to relive painful memories from their past. Later, Nezbitt—disguised as Tristan—kidnaps Mokuba, who is then held captive by Noah while Kaiba faces Leichter in a Duel. After Kaiba's victory, Noah brainwashes Mokuba, erasing his memories of Kaiba and their friends in an attempt to divide them.
During Kaiba’s Duel against Noah, Kaiba gains the upper hand, but Noah uses Mokuba as a human shield, placing him between himself and his monster. Kaiba is unable to attack, unwilling to risk harming his only remaining family member, allowing Noah to seize control of the Duel. However, Kaiba ultimately breaks through to Mokuba using his Blue-Eyes White Dragon, snapping him out of Noah's control. Mokuba escapes Noah’s grasp, and Kaiba activates Last Turn. Kaiba selects Blue-Eyes White Dragon, while Noah chooses his Deck Master, which contains Shinato, leading to Kaiba’s defeat. Mokuba rushes to his brother, but before they can reunite, Noah turns them both to stone.
Following Noah’s defeat at the hands of Yami Yugi, Noah pretends to help the group escape from the Virtual World, claiming to oppose his father, Gozaburo. However, Noah betrays them, attempting to escape using Mokuba’s body. After a change of heart, he returns to stop Gozaburo from taking Kaiba’s body instead. Ultimately, Mokuba, Kaiba, and Yugi successfully escape before the Virtual World is destroyed.
Battle City Finals
Mokuba continues to support his brother throughout the Battle City finals. He watches Kaiba Duel Yami Yugi and is devastated when his brother loses. He also witnesses Kaiba’s match against Joey and is impressed by Joey’s skills, though Kaiba ultimately wins. Despite Kaiba’s usual detached demeanor, Mokuba questions his brother’s emotions and manages to convince him to stay and watch Yami Yugi’s final Duel against Yami Marik.
Pyramid of Light
Mokuba continues to support Kaiba, assisting in preparations for his brother’s Duel against Yugi. He is also tasked with escorting Yugi to the Duel arena. Notably, Mokuba is one of the few people who recognize the change in Kaiba’s behavior and is deeply concerned for him.
Waking the Dragons
Mokuba remains by Kaiba’s side throughout the Waking the Dragons arc. He accompanies his brother during his Duel against Alister and later during the Duel against Dartz. After Kaiba’s first Duel with Alister, Mokuba speaks with him about his lingering hatred toward Gozaburo. When Kaiba loses to Dartz and his soul is taken, Mokuba is left in tears, devastated by his brother’s fate.
Grand Championship
Mokuba plays a key role in organizing the Grand Championship, personally inviting Yugi and his friends and assisting them throughout the event. He also secretly arranges for Yugi’s grandfather to enter the tournament as a challenger, wanting to test Joey’s growth as a Duelist.
Dawn of the Duel
In Dawn of the Duel, Yami Bakura sends Mokuba’s soul to the Shadow Realm to lure Kaiba to Egypt. Mokuba remains unseen until he notices Blue-Eyes Ultimate Dragon in the sky, which leads him and Roland to track Kaiba’s whereabouts. He later watches Yugi defeat the Pharaoh and escapes the collapsing building where their Duel takes place.
The Dark Side of Dimensions
Mokuba participated in the excavation of the Millennium Puzzle from the Shrine of the Millennium Stone in Egypt. During Seto’s Duel against Diva, he summoned Obelisk the Tormentor, triggering the security system’s timer to deactivate the laser field around the Puzzle’s container. Seizing the opportunity, Mokuba swiftly took the container and escaped via helicopter. When Diva attempted to stop him, Mokuba headbutted him away, though Diva managed to snatch two pieces of the Puzzle before Mokuba got away.
Later, Mokuba piloted the helicopter to retrieve Seto after he demanded Yugi enter his tournament for the missing Puzzle pieces. Following Diva’s capture, Mokuba interrogated him about how to extract the hidden piece from the Quantum Cube. Despite Diva’s taunts about their inability to retrieve it, Mokuba remained unfazed and coolly revealed that they had already identified the second missing piece, which was in the possession of Diva’s sister, Sera—though he strategically withheld the fact that she had already entrusted it to Yugi.
At the exhibition tournament, Mokuba observed Yugi’s Duels against both Diva and Seto, noting that the former had turned into another Dimension Duel, similar to what occurred at the excavation site. He later experienced Dark Diva’s disintegration of the world before the Pharaoh returned to aid Yugi in his victory. Afterward, Seto took possession of the Quantum Cube and used it to create a Duel Dimension system aboard his space station. As Seto prepared to use the system to reach the Pharaoh in the afterlife, Mokuba cautioned him to be careful. Before departing, Seto entrusted Mokuba with the leadership of KaibaCorp.
Yu-Gi-Oh! GX
Mokuba appears briefly in Yu-Gi-Oh! GX during Jaden’s flashback of a KaibaCorp card illustration project.
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