In a certain parallel world the demon king Avalon reigns over the last dungeon. No one could defeat him, so for ten thousand years he had been unable to fulfill his life’s purpose. Out of boredom and resignation, Avalon reincarnated into another world in search of someone who can defeat him, but what awaited him there is the body of Akari, a high school girl who was bullied to death.

A dozen years ago, gates suddenly opened on Earth, and monsters from dungeons invaded. Akari, who attended a school that trained “Hunters,” was bullied for being ranked E, the lowest rank in history.

Hoping to find someone stronger than himself, Avalon decides to attend the school as Akari, but those around her don’t realize that she has been replaced by the strongest last boss, and they start bullying her….!?