Kyousuke Kamiya, a high school student, is wrongfully accused of being a notorious mass murderer known as the "Butcher." Despite his protests of innocence, he is sentenced to death. However, instead of execution, Kyousuke is sent to Purgatorium Rehabilitation Prison Academy, a facility designed to rehabilitate criminals through education. The academy is a grim, prison-like environment where students are treated as inmates, and survival often depends on navigating its harsh rules and dangerous inhabitants.

Upon arrival, Kyousuke is placed in a class filled with infamous female criminals, each with their own violent tendencies and dark pasts. Among them are Eiri Akabane, a sadistic serial killer; Renko Hikawa, a bomb-making terrorist; Mai Mashiro, a former idol turned arsonist; and Ayaka Kagari, a mysterious and aloof girl with a reputation for extreme violence. Kyousuke quickly realizes that his new classmates are as dangerous as they are unpredictable, and his survival hinges on avoiding their wrath while trying to prove his innocence.

The narrative unfolds as Kyousuke attempts to adapt to life in the academy, forming uneasy alliances with his classmates. Despite their violent tendencies, the girls gradually reveal more about their pasts and motivations, adding depth to their characters. Kyousuke’s interactions with them oscillate between comedic and tense, as he navigates their volatile personalities and the academy’s oppressive environment. The story explores themes of redemption, trust, and the blurred lines between guilt and innocence, as Kyousuke strives to clear his name and uncover the truth behind the "Butcher" murders.

As the plot progresses, Kyousuke and his classmates face various challenges, including internal conflicts, external threats, and the academy’s rigid disciplinary system. The series balances dark humor with moments of genuine tension, creating a unique tone that blends elements of psychological thriller, black comedy, and action. The characters’ development is central to the story, as their relationships evolve and their pasts are gradually revealed, shedding light on their actions and motivations.

The academy itself serves as a microcosm of societal judgment and punishment, with its strict rules and dehumanizing treatment of inmates reflecting broader themes of justice and morality. Kyousuke’s journey is one of survival and self-discovery, as he confronts not only the dangers of the academy but also the prejudices and assumptions that led to his wrongful conviction. The series concludes with a resolution that ties together the central mysteries and character arcs, providing closure while leaving room for reflection on its themes.