Bullies frequently pick on those who are frail and weak—someone exactly like Yuugi Mutou. His childhood friend, the beautiful Anzu Mazaki, often defends him, but he cannot rely on her forever. Katsuya Jonouchi, usually accompanied by his verbal sparring partner Hiroto Honda, does not seem like a bad person either, even though he always brings Yuugi trouble. Above all, Yuugi longs for a true friend who understands him and would never betray him.
Yuugi treasures his Millennium Puzzle, an ancient Egyptian artifact that ended up in his grandfather's game shop. Believing that solving the puzzle will grant his wish, he completes it, unleashing a new personality within him—the soul of the "King of Games."
Dark, twisted, strong, and dependable, this new personality, named Yami Yuugi, is the complete opposite of Yuugi. Whenever an injustice is done to him, Yami Yuugi takes over Yuugi's body and forces the opponent into a "Shadow Game." The stakes are high, as the loser must taste the darkness that resides within their own heart.