Asato, a high school student with a strong sense of justice, begins investigating a series of minor pranks occurring around the school. His search leads him to the newly appointed school nurse, Egou Nemu. Nemu is admired by the entire student body for her striking beauty, yet she maintains a cold and distant demeanor toward everyone. When Asato accidentally discovers a secret about Nemu, she invites him to her home. There, she reveals a seductive and affectionate side completely unlike her daytime persona, but also a far more dangerous secret: she has already killed someone.

As Asato becomes increasingly entangled in Nemu’s double life, his own moral compass is tested. Their secret is soon uncovered by a Japanese language teacher, Urushibara. Instead of removing the threat, Nemu and Asato manipulate Urushibara into becoming an accomplice, only to learn that Urushibara harbors a shocking secret of their own.

Tension escalates when a student named Shinto begins sniffing around the disappearance of a delinquent whom Nemu killed. Fearing exposure, Nemu and Urushibara devise a plan to murder Shinto during the school’s sports festival. Asato, still clinging to his sense of justice, attempts to stop the plot. On the day of the festival, however, Nemu sets in motion a catastrophic event that draws all parties into a violent and psychological confrontation.