Momonga is an average salaryman who spends his free time playing Yggdrasil, a DMMO-RPG (Dive Massively Multiplayer Online Role-Playing Game) well-known across Japan for its immense world and limitless customization. Unfortunately, all good things come to an end, and Yggdrasil's servers shut down in the year 2138. Wanting to witness the game’s final hours, Momonga, the leader of the guild Ainz Ooal Gown, logs in for the last time and heads toward the guild’s headquarters.

After reminiscing about his comrades and adventures, Momonga prepares for the server to automatically log him out as the clock strikes midnight. However, he is not forcefully booted out of the game. Instead, he finds himself in a new world—now trapped in the body of his avatar and where non-player characters are aware of their feelings.

Left with no other options, Momonga takes on the name of his guild in hopes that other players would recognize Ainz Ooal Gown. Determined to make sense of the bizarre situation, Momonga embarks on a journey to unravel the mysteries hidden in this uncharted world.