Asuna Sugihara, a modest transfer student, arrives at the elite Saint Rei Seine academy, where she is immediately intimidated by the powerful Student Government President, Yurika Ichinomiya. After witnessing Yurika's sadistic side and suffering a traumatic assault on campus, Asuna is lured into joining the student government under the guise of protection. However, she soon discovers that Yurika's kindness was a trap designed to isolate her and claim her as a personal toy.
Asuna is forced into a life of submission as a "Culy" under the cruel command of Mistress Yurika, who uses a pleasure-inducing device to humiliate her in public. When her friend Yoko attempts to rescue her, Yurika orchestrates a sadistic scene that ends in tragedy when Yoko falls to her death. Consumed by grief and hatred, Asuna is pushed to her breaking point and swears a solemn oath to avenge her friend and bring down the sadistic mistress.