"Yu-Gi-Oh! Millennium World" is the final story arc of the original "Yu-Gi-Oh!" manga series, written and illustrated by Kazuki Takahashi. The narrative centers on Yugi Mutou and his friends as they are transported to ancient Egypt, where they uncover the origins of the Millennium Items and the Pharaoh's lost memories. The story delves into the Pharaoh's past life as Atem, the ruler of ancient Egypt, and his battle against the dark sorcerer Zorc Necrophades, who threatens to plunge the world into eternal darkness.

The arc begins with Yugi and his companions deciphering the ancient text on the Stone Tablet, which reveals the Pharaoh's true name and his connection to the Millennium Puzzle. This discovery triggers a mystical event, transporting the group to the ancient Egyptian kingdom. There, they learn that the Pharaoh's soul was sealed within the Millennium Puzzle to prevent Zorc's resurrection. The narrative intertwines the modern-day characters with their ancient counterparts, revealing their roles in the Pharaoh's past.

Atem, the Pharaoh, must reclaim his memories and confront his past mistakes, including the betrayal of his high priest, Akhenaden, who becomes corrupted by the power of the Millennium Eye. Akhenaden allies with Zorc, seeking to overthrow Atem and unleash chaos. The story explores themes of destiny, sacrifice, and the struggle between light and darkness, as Atem and his loyal priests—Seto, Mahad, Karim, Shada, and Isis—fight to protect the kingdom.

The climax of the arc revolves around a high-stakes Shadow Game between Atem and Zorc, with the fate of the world hanging in the balance. Yugi and his friends play a crucial role in supporting Atem, using their knowledge of modern-day Duel Monsters to aid in the battle. The resolution sees Atem confronting his own guilt and accepting his responsibility, leading to a final duel between Yugi and Atem to determine who will claim the title of the true King of Games.

The arc concludes with Atem's soul finding peace and departing to the afterlife, while Yugi and his friends return to the present, forever changed by their journey. "Yu-Gi-Oh! Millennium World" ties together the series' overarching themes of friendship, legacy, and the enduring power of games as a means of connection and resolution.