In 2126, a Full-Dive Massively multiplayer online role-playing game or DMMORPG called YGGDRASIL was released, standing out among all other DMMORPGs due to its unusually high ability for the player to interact with the game. After an intense twelve-year run, the game servers are about to be shut down. Within the game exists a guild, Ainz Ooal Gown, once consisting of 41 members and credited as one of the strongest guilds in the game. Now only four of the members remain, the other 37 having quit the game, and only one, you, a skeletal Lich "Overlord" character named Momonga, continues to play as the guild leader, maintaining their headquarters in The Great Tomb of Nazarick. In the minutes before the shutdown you invited the remaining guild members, but of those only one appears and only for a short while before leaving. While saddened by this, you accepted the reality that your friends have their other lives to take care of and decides to stay logged in until the servers shut down.

When the shut-down time arrives, you discovers that the game hasn't vanished; instead, it appears as if Nazarick has been transported to another world altogether and its various NPCs becoming actual living beings. You has been trapped in the form of your game avatar, leaving you unable to use the normal player functions such as General Message, or even log out. With no other option, you set out to learn if any players like yourself are in this new world. Taking on the name of the guild, Ainz Ooal Gown, as a message to any other remaining players, you began exploring the world in an attempt to figure out what has happened while searching for anyone or anything that could help you solve this mystery, while ensuring the safety of Nazarick.