That day, Sayo Mitsurugi wasn't focused on her lessons, due to staying up late the previous night. During the lunch break, she was talking on the phone with her hospitalized younger brother, and up until that moment, everything was part of her usual routine. But then. Suddenly, the signal cut off, and the phone call ended. From that moment on, hell began! Due to the influence of zombies that appeared in the school, the men began to transform into monstrous beings one after another. By chance, Saya teams up with her classmates, the angelic Maria and Momo, to attempt an escape from this hell!