Imori's grandfather was a game collector and left him books about games and ancient Egypt. While reading one of them he learned about the Millennium Item, an item in the possession of his classmate, Yugi Mutou. The book stated "The one who solves the Millennium Puzzle shall gain the thousand ways of the Shadow Games and become the Guardian of Darkness." Imori noticed that Yugi was often bullied until he began wearing the Millennium Puzzle and deduced that Yugi had acquired the powers of darkness. He swore to himself that he would defeat Yugi and take his place as the Guardian of Darkness.
Imori's grandfather had acquired the Dragon Cards game in Manchuria, during World War II. Imori eventually found them in his garden shed, but did not know exactly what they were. He brought them to Yugi's family's game shop, Kame Game, to ask if Sugoroku Mutou had any knowledge on the game. Yugi had not spoken much to Imori before and thought this could be a chance to make friends with him. Sugoroku recognized the game and was insistent that its seal was not to be undone. He explained that with the cards and seal, represented by yin and yang respectively, they were currently in balance, but breaking the seal would cause a disrupt that and cause a warped power. Sugoroku asked Imori to promise not to break the seal. He lied that he would not, but was secretly fixated on the power of shadows that Sugoroku said had been sealed.
After leaving the store, Imori did further research on the cards. He learned that once the seal is broken, a Shadow Game must be played or the people of the land will suffer eternal disaster and the loser of the Shadow Game must offer their soul to the soul-eating jar to calm the wrath of the dragons. He learned the rules of the card game and studied them to the point where he was confident he knew all the ways to win. With this knowledge, he plotted to defeat Yugi in a Shadow Game to usurp the power of the Millennium Puzzle.
A few days after visiting the store, while their class were swimming, Imori stole the Millennium Puzzle from the changing room and left Yugi note, instructing him to come to Room C alone. When Yugi arrived, Imori told him what he knew about the Millennium Puzzle and of his intentions to usurp its power. He then broke the seal on the Dragon Cards, forcing Yugi to accept a Shadow Game. With his vast knowledge of the game and Yugi unable to access the puzzle, Imori was confident he would win their game.
Judging by the cards Yugi discarded during the game, Imori deduced he was trying to summon a Huo Long and a Jin Long, the fire and metal dragons. To counter them Imori gathered the cards needed to summon two Shui Long, the water dragons. With fire weak to water and water strengthened by metal, Imori easily won and Yugi's soul was pulled into the soul-eating jar.
Before collapsing, Yugi grabbed the puzzle, causing Dark Yugi to come out. Dark Yugi staked his soul to challenge Imori to another game. Imori figured he would need to defeat Dark Yugi too in order to become the Guardian of Darkness, so he accepted.
Again, Imori was able to figure what dragons his opponent planned on summoning. Knowing Dark Yugi planned on summoning the Level 4 earth dragon, Tu Long and Level 5 metal dragon, Jin Long, Imori gathered the cards to summon the Level 5 water and wood dragons, Shui Long and Mu Long. With his water dragon strengthened by the metal dragon, Imori got it to attack, but with earth empowering metal, Dark Yugi got his earth dragon to create a dam to block the attack. Imori's water dragon strengthened his wood dragon, which attacked the earth dragon, by draining its power via its shoots. The water dragon attacked the metal dragon, but having given its strength to the wood dragon, only succeeded in weakening the metal dragon. The metal dragon sliced the wood dragon apart before being defeated by the water dragon. The freed earth dragon, shattered the ground, causing the water dragon to sink into an abyss.
Having lost the game, Imori's soul was sucked into the soul-eating jar, to be eaten by twenty five dragons. Since the jar could only hold one soul at a time, Yugi's soul was freed.
The second Dragon Cards game ended with Imori losing. Imori's soul was then sucked into the soul-eating jar, to be eaten by twenty-five dragons, while Yugi's soul came out and was re-absorbed into his body unharmed.
|Yugi Mutou||Dragon Cards (game)||Win||46|
|Dark Yugi||Dragon Cards (game)||Lose||47|