Mokuba Kaiba

Mokuba Kaiba is Seto Kaiba's younger brother.

Personality
At the beginning of the manga, Mokuba is very mean and will go as far as trying to trick Yugi Muto to get back at him for defeating his older brother, Seto Kaiba. Mokuba is another good game player 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 second series of the 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.

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).

In the second series Yu-Gi-Oh! anime (Yu-Gi-Oh! Duel Monsters), 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 a 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 consistantly care about more than anyone or anything.

Orphanage
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.

In the second series anime, 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.

Although Mokuba was insistently happy at the orphanage, Seto had always aspired greater things for both of them and looked to the future.

Adoption
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 had won by cheating in the manga. In the anime, he 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.

Capsule Monster Chess
In the manga, Mokuba leads a gang of followers his age. With them, he plans to beat Yugi in a game to get revenge for him beating his brother in Duel Monsters and inflicting a Penalty Game on him.

Mokuba gets Old Man Dentures to rig his Capsule Monster Chess coin machine. He and his gang later arrive at Old Man Dentures store to meet Yugi at the coin machine. After introducing himself as Seto Kaiba's brother, to Yugi, he has his followers seize Yugi to force him into a game. They proceed to take Dentures coin machine. Dentures acts mad at first, but allows them to carry on after Mokuba drops a large amount of money in front of him.

The gang take Yugi and the dispenser to their hideout, where he must play Capsule Monster Chess against Mokuba. As Mokuba hoped, Yugi changes to Dark Yugi for the game. The rigged dispenser gives Yugi mostly low Level monsters and Mokuba mostly high Level ones. They accept the stakes that if Mokuba wins, he gets to cut off one of Yugi's fingers and if Yugi wins, Mokuba will have to play a Penalty Game.

Dark Yugi makes the game a Shadow Game. Throughout it, he sacrifices his monsters to draw Mokuba's into a diagonal line and uses his last monster "Torigun" to take Mokuba's remaining four monsters all out at once.

For Mokuba's Penalty Game, he is made believe that he is trapped inside a giant Capsule Monster Chess capsule. Before the capsule has Mokuba fully engulfed, Mokuba warns Yugi that Death-T is coming.

This did not happen in the first series anime. Instead, Yugi faced Warashibe in a similar game of Capsule Monster Chess.

Planning Death-T
During the planning of the theme park Death-T, Mokuba insisted on facing Yugi in one of the stages. Although Seto advised against it, they still went through with it. The two of them also made a bet over which stage Yugi would die in. Mokuba bet Death T-4, while Seto bet Death T-5.

Russian Roulette
When Kaiba's chauffeur brings Yugi and Jonouchi to their mansion, Mokuba meets them in the car. He introduces himself as the vice-president of KaibaCorp and tells Yugi his given name for the first time. He tells Yugi not to worry as they will be giving him V.I.P. treatment for the grand opening of Kaiba's new secret project, but still keeps a suspicious air about himself.

At the mansion, Mokuba invites Yugi and Jonouchi to a meal, featuring the best food in the world. However the meal turns out to be six servings of a meal a spoiled young child would like. He suggests that they take turns spinning the turntable that the food is on and eat the meal that lands in front of them. He lies that there isn't poison in them and claims that there is a treasure hidden in one.

Jonouchi goes first and Mokuba uses a hidden switch in a syrup bottle to give him a poisoned meal. He admits to lying and introduces the meal as a game of Russian Roulette Dinner. He forced Yugi to continue to win the antidote to save Jonouchi.

Yugi switches to Dark Yugi, who figures out how Mokuba is cheating and manages to smash the syrup bottle, giving Mokuba a poisoned meal. Mokuba eats it and loses, handing the antidote over to Yugi. Mokuba falls over poisoned, while the butler rushes to his aid.

Death-T
The next day, Mokuba prepared to face Yugi in a game of Capsule Monster Chess, during Death T-4. He confronted Seto about their bet on which stage Yugi would die on. He pointed out that Seto bet Yugi would die in Death T-5, meaning he bet Yugi would beat Mokuba. Seto stood by his choice, said that Mokuba cannot beat Yugi and reminded Mokuba of how he tried and failed to show him up by beating Yugi in a game before. Mokuba hung his head and said that he thought Seto would like him, if he beat Yugi. Seto yells at Mokuba that there is no room for brotherly love in the world of gaming and until Mokuba realizes that, he will always be a loser. Mokuba stormed off to face Yugi, eager to prove Seto wrong.

Mokuba rigged the Capsule Monster dispenser again, but still lost. Seto, held no sympathy for his brother and subjected him to the "Experience of Death" Penalty Game, as per Death-T rules. However Dark Yugi returned and saved Mokuba from the grisly punishment. Mokuba was surprised that Yugi saved him and asked why. Yugi replied that he wouldn't have won, if he didn't have his friends supporting him. This causes Mokuba to reflect on his past and how Seto had changed since they left the orphanage. He wonders if Yugi can help Seto when he faces him in the next round.

Thankful for Yugi saving him, Mokuba rescues Yugi's friend Honda, who had been trapped in the previous stage of Death-T.

Duelist Kingdom
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. 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 (which he ends up surviving), 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 (cunningly disguised with a hat and a bandit-like handkerchief) 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.

Yugi begins to preach, but he looks up and realizes Mokuba has disappeared. Mokuba reappears next to Yugi and steals 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 deep, dark 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. Seto gains an advantage through Crush Card and Blue-Eyes Ultimate Dragon and is set to win, when Yami counters with an indestructible wall of Kuribohs through Multiply, keeping his life points safe. Yami then backs him into a corner by "fusing" his Mammoth Graveyard with Ultimate Dragon, making it decay and lose 1200 attack points each turn because they couldn't properly fuse. 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. Not wanting to see Seto die, Yugi allows him to win the duel, only to see Seto lose his soul to Pegasus after Tea won Yugi the right to enter into the main castle. In the end, Mokuba gets his brother back, and Yugi wins his soul back as well.

Battle City
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 duels, his brothers use 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. Mokuba does not end up prosecuting the Robas, commenting that Big Brother stories get him every time.

As Mokuba walks away, he's set upon 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 English anime 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 build a tower of boxes, and Mokuba manages to escape, but Téa is captured before she manages to. Mokuba takes a helicopter to pick his brother up.

Virtual World
During the Virtual World arc Mokuba and his brother are taunted by Noah as he shows them images from their past. Later on, Nesbitt, disguised as Tristan, kidnaps Mokuba where he is held captive by Noah while Kaiba faces Lector. After Kaiba wins the duel against Lector, Noah brainwashes Mokuba in an attempt to split them up. In the duel between Kaiba and Noah, Noah uses Mokuba as a shield in order to defend himself from Kaiba's attack with "Twin-Headed Thunder Dragon". Eventually Kaiba manges to break through to Mokuba using his "Blue-Eyes White Dragon" card. Unfortunately Noah turns them both to stone before they can be reunited. After Noah's defeat against Yami Yugi, Noah tries to help the gang to escape from the Virtual World after Gozaburo reveals his plans. However, Noah tricked all of them to escape using Mokuba's body. However, after a change of heart, Noah comes back to the Virtual World to stop his father from taking Seto's body. Then Mokuba, Seto and Yugi leave the Virtual World before it explodes.

Battle City finals
Again, Mokuba continues to be a supporting character. He's also present when Kaiba and Joey have their duel and witnesses Joey putting up a good fight, but ultimately Seto wins. He also questions his brother's emotions as well and convinces him to be there when Yugi faces Marik in the finals.

Waking the Dragons
Mokuba is a supporting character through this arc. He is with Kaiba during his duels with Alistair and is present during Kaiba and Yami's duel with Dartz.

Dawn of the Duel
Mokuba was knocked unconscious by Bakura and he wasn't seen again until the beginning of Yugi and Atem's final duel where he and Roland tracked Kaiba to Egypt.

Deck
Mokuba was not seen using his own Deck in the anime and manga series, but in the video games, he would play with an animal themed Deck. Some of his Spell and Trap Cards involve kid-themed items, reflecting his naive nature.

In Yu-Gi-Oh! Worldwide Edition, he used to play a deck with only monsters and Polymerization. Sometimes he would have gained Blue Eyes Ultimate Dragon as well. He plays everything in attack mode then.

Capsule Monster Chess pieces
The first time Mokuba faced Yugi, he used the following Capsule Monster Chess pieces:
 * Head Sucker
 * Gumbo
 * Cobrada
 * Dinosaur Wing
 * The Skull

When he faced Yugi in Death-T, he used the following:
 * Megaton
 * Nama Hargen
 * Big Foot
 * Zoid "M"
 * Armorsaurus