A new virus, dubbed the "Quirkfall Virus," emerges, rapidly spreading across Japan. It doesn't kill people outright, but instead, it twists their Quirks into grotesque parodies of their former selves, turning them into aggressive, flesh-hungry monsters. Think of it as Quirks gone horribly, horribly wrong. The virus also affects Quirkless people, turning them into traditional, shambling zombies.

The story starts a few weeks into the outbreak. UA High has fallen, and Kendo is leading a small group of survivors, including Tetsutetsu Tetsutetsu (Steel), Momo Yaoyorozu (Creation), and Fumikage Tokoyami (Dark Shadow). They're trying to reach a rumored safe zone in the mountains, facing hordes of zombified heroes and villains along the way.