At the beginning of the manga, Mokuba was very mean and would go as far as trying to trick Yugi Mutou to get back at him for defeating his older brother, Seto Kaiba. Mokuba is a gamer who specializes in Capsule Monster Chess (Capmon), but is not as good of a gamer as his brother. He is so committed to avenging his brother's humiliation, he uses several extreme measures, such as having his friends brandish a machine gun, a knife, and a stun gun in one manga chapter to coerce Yugi to play Capsule Monster Chess with him.
In the Yu-Gi-Oh! Duel Monsters anime, Mokuba is eternally devoted to his brother Seto Kaiba and is constantly by his side. He is more naive and good-natured, and will do whatever his brother tells him to. He also seems to trust Yugi and his friends more than he did previously. There is a part in one episode when he saw (Yami) Yugi watching him from another building when he was about to kick some brothers out of the Battle City grounds, when he considered, "You know, I bet Yugi would give them another chance!" He must really respect Yugi as he starts to think like him.
In the original Japanese version of the Yu-Gi-Oh! manga, Mokuba tends to omit honorifics when referring to people other than his older brother. He also has a habit of calling Jonouchi "Jōnouchi no yarō"; (that bastard Jonouchi). Mokuba politely refers to his older brother as "nii-sama" (honorable older brother). He is very forgiving, especially to his brother. Even after Noah hypnotized him, and brainwashed him into forgetting who Seto and the others were, Mokuba forgave him and treated him like a brother (they are actually step brothers).
In the Yu-Gi-Oh! Duel Monsters anime, Mokuba is a kind-hearted boy who is naïve to the ways of the world. He succeeds in befriending Yugi and his friends; his brother does not approve of this. Mokuba does not Duel in the first series anime. He only Duels in the second series and manga. Mokuba has an unlucky streak of being kidnapped by Seto's enemies forcing Seto to show his kinder side and rescue him, and is, in fact, the only person his brother is shown to consistently care about more than anyone or anything.
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At a young age, Mokuba and Seto were orphaned. Their actual surnames are unknown. Their mother died when Mokuba was born. Their father died supposedly in an accident when Seto was eight. Their relatives used up their inheritance and left them at the city orphanage.
Seto was bright and intelligent, which led to many prospective parents wanting to adopt him, but Seto swore to protect his brother at all costs, and wanted Mokuba adopted with him, which all had refused. Whenever bullies would pick on Mokuba, Seto would always stick up for him, including jumping a child to get back a toy plane that he had taken from Mokuba.
Although Mokuba was insistently happy at the orphanage, Seto had always aspired greater things for both of them and looked to the future.
When the former head of Kaiba Corporation, Gozaburo Kaiba, arrived at the orphanage to perform a publicity stunt, Seto saw the chance to challenge him to a game of chess, with Gozaburo forced to adopt Seto and Mokuba should he win. Mokuba was five at the time. Seto won by studying Gozaburo's chess methods.
Six years later, Seto took over the company. In the second series anime, it showed that he had used Mokuba to do so. Seto planned gaining 51% of the company in order to overthrow Gozaburo. Seto deliberately leaked this information to Gozaburo and accused Mokuba of telling Gozaburo. Mokuba sided with Gozaburo, who allowed Seto to gain 49% of the company, believing that Mokuba would give him his 2%. Gozaburo was fond of making his enemies think they were winning against him so they would look worse when he beat them, which Seto based his plan around. As Seto planned, Mokuba switched sides last minute giving his 2% to Seto. Mokuba stated that he would never go against his elder brother.
Mokuba was originally imprisoned by Pegasus on a high tower in Duelist Kingdom, in order to force Seto Kaiba to come and Duel Pegasus to rescue Mokuba (in the Japanese version, he wanted the card that holds secret information about KaibaCorp that Kaiba entrusted to him). However, Mokuba escapes from the tower by a rope of knotted bedsheets, which only go a small way down the tower. After a rather nasty fall, Mokuba steals a boy's Deck and his star chips, leaving him to be kicked off the island. Yugi and his friends find the boy and promise to help him. They go back to the scene of the crime. Mokuba jumps out of the bushes and challenges Yugi to a Duel. The only cards he played were "Man-Eating Plant" and "Krokodilus". Mokuba's identity then gets found out, and he explains that after Yugi beat Seto in a Duel, his brother had gone away and abandoned him, and that it was all Yugi's fault. Mokuba reappears tries to steal his star chips. Yugi gets Mokuba to see the error of his ways, and they all run to try and not let the boy get kicked off the island. All they succeed in doing is getting Mokuba captured again. Yugi agrees to Duel for his freedom, and wins. But Pegasus's thug, Kemo, takes Mokuba anyway, and lock him in a dungeon.
Seto reaches him, and just as he is about to free Mokuba, Pegasus shows up and steals Mokuba's soul, forcing Seto to Duel Yugi in a largely unfair match with Mokuba's soul on the line. In desperation, Seto backs away to stand at the castle's edge, telling Yugi he will die with his dragons, implying that if he couldn't save Mokuba, his life wasn't worth living. (In the dub, Seto backed on to the ledge, knowing Yugi wouldn't attack him and let him get hurt, therefore letting Kaiba win the match). Not wanting to see Seto die, Yugi allows him to win the Duel, only to see Seto lose his soul to Pegasus after Téa won Yugi the right to enter into the main castle. In the end, Mokuba gets his brother back, and Seto wins his soul back as well.
Seto and Mokuba come back from Duelist Kingdom and go back to KaibaCorp. Seto goes straight to the Big Five to get revenge on them for what they did to him and Mokuba. They manage to convince him that they did what they did to help Kaiba, not hurt him. To prove this, they tell him that they have finished the virtual world simulator that they had been working on. Kaiba, who became very eager to test it out, decided to wait to fire them after he tested the simulator. Mokuba was very against it, but Kaiba decided to do it anyway. While inside, it became very apparent to Kaiba that the Big Five had rewired the simulator and he became caught by a ninja.
Mokuba, realizing it was a trap, swiped Kaiba's Deck from the chair and ran to get help. He recruited Yugi and his friends to help him. They went to Kaiba's personal lab for more chair simulators to get into the virtual world. Mokuba, Yugi, and Joey entered the world while Tea and Tristan stayed behind to stand guard.
When inside, they first enter a graveyard where they run into 3 monsters. Mokuba shows Yugi and Joey how to summon a monster. They then run into a fairy Named Earu, that leads that to an old town. In there, Yugi suggests they split up to look around the town for clues about Kaiba. An old lady told Mokuba that she saw someone with a prisoner going towards a mountain and the only way to get there was to cross a large desert.
They tried crossing the desert that’s after the town but get hit by a twister. They all end up back at the town with Mokuba shaken from the twister. An old man tells them that to cross the desert they need a special monster, a Niwatori card. In order to get it they must enter a tournament and win against the champion, Madame Butterfly. Joey goes up against the champ using the name Senor Porky. The champion turns out to be Mai, then she realized it’s Joey. She decided to help them out by getting the card by force and the running for it. While crossing the desert, they ran into a monster but Joey got rid of it.
When they finally reached the temple after the desert Mokuba runs towards it, desperate to see his brother again. when everyone catches up to him they open a door inside the temple and see a maze. they soon hear a girl scream, making Joey run to help her. However, they are all ambushed by labyrinth tanks and only manage to escape thanks to Yugi using Magical Hats. they then see Iru again and it led them to a princess named Adina, who looks exactly like Mokuba (except a girl). They then find the exit but it is blocked by a Gate Gaurdian. Yugi and Joey defeat it using Polymerization on Red-Eyes Black Dragon and the Summoned Skull and then adding Dragon Nails.
Adina, thankful that they had saved her, took took them to her castle where they discussed the Heroes of Legend. Soon, however, the castle is surrounded by monsters. One of them captures Mokuba, who was dressed up like Princess Adina and then taken to the castlein the sky, to where Kaiba is.
Upon meeting his brother, Mokuba set him free and gave back his Deck. Kaiba disapproved of Mokuba asking Yugi for help and wasn’t thankful to Yugi, Joey, or Mai. Unfortunately, the Big Five decide to make the Mythic Dragon appear even though there were no sacrifices. The dragons first target is the person who doesn’t have any monsters to defend himself with: Mokuba. Joey, however, ordered his Red-Eyes Black Dragon to take the hit therefore losing the game and disappearing. Then Mai gets hit and is taken. Yugi tries to convince Kaiba work with him by summoning his Blue-Eyes Ultimate Dragon but Kaiba refuses. The Mythic Dragon goes to attack Kaiba, but Mokuba, the only one realizing that the attack was for Seto, pushed Seto out of the way but got hit, leaving his brother devastated.
In the end, Kaiba and Yugi worked together and defeated the mythic dragon. Afterwards, Adina turns out to be the Mystical Elf, and brought back Joey, Mai, and Mokuba. Reunited at last , everyone left the virtual world.
During the Battle City tournament, Mokuba is the Battle City commissioner, calling violations and penalties when needed. While his brother Duels, Mokuba wanders around town. The first violation he sees is performed by the Roba brothers. While the eldest, Espa dueled, his brothers used binoculars to see his opponent's hand. Mokuba tackles Espa's brother, and is about to throw Espa out when the younger Robas tell Mokuba about how their big brother protects them from bullies by winning Duels. This reminds Mokuba of his relationship with Seto, and he does not disqualify the Robas, commenting that big brother stories get him every time.
As Mokuba walks away, he is ambushed by Rare Hunters and kidnapped. He is tied up and dangled from a helicopter, which flies over his brother's head. The Rare Hunters make Seto Duel with Yugi against infamous tag team Duelists Lumis and Umbra. The loser of the Duel would plummet to their death (In the dub they would be sent to the Shadow Realm). While they Duel, Mokuba is taken to a warehouse, and locked up there with Téa. Together, they construct a tower of boxes, and Mokuba manages to escape, but Téa was captured before she managed to escape. Mokuba was ordered to go find Yugi and Seto. Kaiba's younger brother took a helicopter to pick his brother up.
During the Virtual World arc, Mokuba and Seto are taunted by Noah as he showed them images from their past. Later on, Nezbitt, disguised as Tristan, kidnaps Mokuba where he is held captive by Noah while Kaiba faces Leichter. After Kaiba wins the Duel against Leichter, Noah brainwashed Mokuba, who forgot who Seto and his friends are, in an attempt to split them up. In the Duel between Kaiba and Noah, Seto was about to win the Duel when Noah used Mokuba as a shield by putting him between Noah and Noah's monster, so that Mokuba would be harmed by the attack should Seto choose to do so. Kaiba was unable to bring himself to harm his last living family member, allowing Noah to get the lead in the Duel. Eventually Kaiba manged to break through to Mokuba using his "Blue-Eyes White Dragon" card, and when Mokuba ran away from Noah Kaiba activates Last Turn. Kaiba picked Blue-Eyes White Dragon, and Noah chose his Deck Master which held the second Deck Master: Shinato, causing Seto to lose the Duel. Mokuba ran to his brother after he lost but unfortunately, Noah turned them both to stone before they could be reunited. After Noah's defeat against Yami Yugi, Noah tried to "help" the gang to escape from the Virtual World after Gozaburo reveals his plans. However, Noah tricked all of them so that he could escape using Mokuba's body. However, after a change of heart, Noah came back to the Virtual World to stop his father from taking Seto's body. Then Mokuba, Seto and Yugi left the Virtual World before it exploded.
Battle City finals
Again, Mokuba continues to be a supporting character. He sadly watched Seto Duel and lose to the Pharaoh. He's also present when Kaiba and Joey have their Duel and witnessed Joey putting up a good fight, but ultimately Seto wins. He also questioned his brother's emotions as well and convinced him to be there when Yami Yugi faced Yami Marik in the finals.
Waking the Dragons
Mokuba is a supporting character through this arc. He was with Kaiba during his Duels with Alister and is present during Kaiba and Yami's Duel with Dartz. Mokuba spoke with Seto after the first Duel with Alister concerning the Duelist's hatred towards Gozaburo and Kaiba. After Seto Kaiba and Yami Yugi's Duel with Dartz, Mokuba tried to go after his older brother, but tea told him to stay.
Mokuba is again a supporting character, having the duties of inviting and helping Yugi and his friends through the whole championship. It is also believed that he was the one who allowed Yugi's grandpa to secretly participate in the championship.
Dawn of the Duel
Yami Bakura sent Mokuba's soul to the Shadow Realm by some unseen means and he wasn't seen again until the beginning of Yugi and Atem's final Duel where he and Roland tracked Kaiba to Egypt. Mokuba watched Yugi defeat the Pharaoh and escaped from the falling building where the two Yugis Dueled.
Pyramid of Light
Mokuba was supporting his elder brother, helping with the preparations for his Duel against Yugi. He was also tasked with bringing Yugi to the arena in the first place. It should be noted that he was one of the few people who noticed the change in Kaiba's behavior and was genuinely worried about him.
Mokuba was not seen using his own Deck in the anime and manga series. The only known cards in the stolen Deck were "Krokodilus" and "Man-Eating Plant". During the Legendary Heroes arc, he used his brother's Deck until Seto was freed.
Worldwide Edition: Stairway to the Destined Duel
In Yu-Gi-Oh! Worldwide Edition: Stairway to the Destined Duel, he used to play a Deck with only monsters and "Polymerization", and always plays his monsters in Attack Position. He also has "Blue-Eyes Ultimate Dragon" as well.
Capsule Monster Chess pieces
The first time Mokuba faced Yugi, he used the following Capsule Monster Chess pieces:
When he faced Yugi in Death-T, he used the following:
|Yugi Muto||8||No result|
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Yu-Gi-Oh! Character Guidebook: The Gospel of Truth: Mokuba Kaiba's profile
- ↑ 2.0 2.1 2.2 "Character". 4K Media Inc.. July 7, 2015. http://www.yugioh.com/characters/mokuba-kaiba.
- ↑ http://movie.naver.com/movie/bi/mi/detail.nhn?code=150117
- ↑ Yu-Gi-Oh! GX episode 62: "A Greater Porpoise"