Bullies often target someone frail and weak—someone exactly like Yûgi Muto. He treasures his Millennium Puzzle, an ancient Egyptian artifact that was brought into his grandfather's game shop. Believing that solving the puzzle will grant him his wish, he completes the puzzle, unleashing a new personality within him, the soul of the "King of Games." The new personality named Yami Yûgi is the exact opposite of Yûgi. Upon any injustice toward him, Yami Yûgi takes over Yûgi's body and forces the opponent into a "Shadow Game".

Nao Kanzaki, a student, was blackmailed into joining a "Liar Game" and ended up losing 100 million yen. In order to repay the debt, she enlists the help of Shin'ichi Akiyama, a genius swindler who was only recently released from jail for bankrupting one of Japan's largest scam companies.

It's the ultimate showdown of wits, brains, strategy, and alliances for a chance to win 500 million won.

The anime centers around a boy named Kouta Kouka (Kouka Kouta in Japanese name order, an apparent wordplay on Coca-Cola). Kouta strives to be the world's best Bottle King at the Bottle Battles in the virtual Drink World. He comes across his Bottleman partner Colamaru and then wages battles with various rivals.

In Big Money City, players participate in "Hero Battles" using Bankfon Gs, which allows them to rent powerful hero suits and fight battles against other players, receiving power boosts from the system's public domain feature. Kaito Goushou, a young elementary school student who is always eager to help others, ends up hastily signing a contract to rent the powerful unlisted hero suit, "Enter the Gold," from a mysteriously seedy priest named Sennen; however, he soon learns that the suit comes with a debt of 10 billion yen, and Kaito must now clear his dues by winning Hero Battles.