When a strange demonic infection suddenly sweeps the globe, every male in humanity is transformed into a zombie. The outbreak begins without warning during a normal school day. High school student Mitsurugi Saya is struggling to focus during class, distracted by worries over her brother who is currently hospitalized. When the infection reaches her school, she watches in horror as one boy after another mutates into ravenous monsters. The male zombies do not simply bite their victims; they attack using grotesque tentacle-like appendages designed to spread the infection further. Saya manages to locate her friends, Amashika Maria and Momoshiro Momo, and the three girls form a team to fight their way through the hordes of zombified male students in a desperate bid to escape from hell on earth. Thanks to her quick thinking and combat skills, Saya leads the group out of the school. They are rescued by a housewife named Arisugawa Chiyo, who possesses a car and firearms. The survivors decide on their next destination: the hospital where Sayas brother is a patient, hoping to find him alive amidst the chaos. The central conflict forces these former schoolgirls to take up weapons and fight for survival in a world where half of humanity has become the enemy, blending intense action with ecchi horror elements.