On the unremarkable little island of "Sheep's Head Island," a prison housing only the most dangerous criminals stands tall. Police officer Takamiya was living a peaceful life until suddenly, the prison escape alarm blares. As islanders flee in panic and are brutally murdered one after another, the police unleash their trump card to solve the case: high school girl Yuka, also known as "The 13 Murderer." On an island with a 0% survival rate, can this merciless girl hunt down the demons?