At Megurigaoka Private High School, a group of girls have made their home in the aftermath of a zombie outbreak that has devastated the world outside. The school’s halls and grounds are now overrun with the infected, but the remaining students have barricaded themselves on the upper floors, creating a fragile sanctuary. Yuki Takeya is a cheerful and energetic girl who believes she is still living a normal, happy school life, attending classes and participating in club activities with her friends. This delusion is a psychological defense mechanism, as the reality of the zombie apocalypse has proven too traumatic for her to bear.

Protecting Yuki from the horrifying truth falls to the other members of the School Living Club. The group includes the reliable and maternal Yuri Wakasa, who acts as the de facto leader, and Kurumi Ebisuzawa, who has armed herself with a shovel and serves as the group’s primary fighter against the zombies. Their fragile routine is disrupted when they encounter Miki Naoki, another survivor hiding in the school’s cafeteria. Initially distrustful and pragmatic, Miki is shocked to discover the extent of Yuki’s delusion and the elaborate charade her friends maintain to keep her sane. The girls must balance their scavenging for supplies and defending their makeshift home with the emotional labor of preserving Yuki’s fractured mind. Their teacher, Megumi Sakura, whom the girls affectionately call Megu-nee, also appears to be part of their group, though her presence carries a tragic and pivotal secret that comes to define the final act.

As the story progresses, the psychological strain on the group intensifies. Kurumi carries a heavy burden of guilt, haunted by a memory of a boy she liked, Tsumugi, who was bitten while protecting her, forcing her to be the one to strike him down. The tension between maintaining the safety of their current shelter and the desire to find other survivors or a more secure location creates conflict, particularly with the pragmatic Miki who questions the sustainability of living in a fantasy. The narrative reaches a climax when a major incident, such as a bell tower ringing and drawing a massive horde of zombies, forces the girls into a desperate final confrontation. In this life-or-death struggle, the illusions protecting Yuki are shattered, forcing her to confront the world as it truly is and accept the loss of her teacher, Megu-nee, whose true nature as a figment of Yuki’s imagination or a lingering spirit is ultimately revealed. The surviving girls must then decide whether to continue clinging to their broken school or finally face the uncertain future beyond its walls.