Yu-Gi-Oh Forbidden Memories, known in Japan as Yu-Gi-Oh! Shin Duel Monsters (遊戯王真デュエルモンスターズ封印されし記憶), is a video game loosely based on the Yu-Gi-Oh! manga and anime series.
The game, made for the PlayStation, takes place in Ancient Egypt. The players play the Yu-Gi-Oh! Trading Card Game alongside characters that appear in the series.
Throughout most of the game, the protagonist is Atem, the Prince of Ancient Egypt. After the high priest Heishin overthrows the Pharaoh, Atem sets out to free Egypt from Heishin’s rule. It is later revealed that Heishin seeks to usher the return of Nitemare, an ancient evil wizard.
Part of the game takes place in modern times. For this part, the protagonist is Yugi Mutou. He is taking part in a tournament when he is tasked by Atem with retrieving relics that the Prince needs to complete his quest, which are held by some of the contestants in the tournament.
The game begins in ancient Egypt, with Prince Atem sneaking out of the palace to see his friends, Jono and Teana, at the dueling grounds. While there, they witness a ceremony performed by the mages, which is darker than the ceremonies that they normally perform. After the ceremony, Atem duels one of the priests, named Seto, and defeats him.
When Atem returns to the palace, he is quickly sent to bed by Simon Muran, his tutor and advisor. As Simon walks away, he is informed by a guard that the high priest Heishin has invaded the palace, using a strange magic. Muran searches for Heishin. When Muran finds him, Heishin tells Muran that he has found the Dark Power, then uses the Millennium Rod to blast Muran. When Heishin finds Atem, he threatens to kill the Egyptian king and queen if he does not hand over the Millennium Puzzle. Muran appears behind Heishen and tells Atem to smash the puzzle. Atem obeys, and Muran seals himself and Atem inside the puzzle, to wait for someone to reassemble it.
Five thousand years later, Yugi Moto reassembles the puzzle. He speaks to Atem in the puzzle, and Atem gives Yugi six blank cards. Not sure what they are for, he carries them into a Dueling Tournament. After he defeats one of the duelers, one of the cards is filled with a Millennium item. Realizing what the cards are for, Yugi completes the tournament and fills all six cards with Millennium items. This allows Atem to return to his time.