A high school teacher named Sakurai, pregnant and deeply committed to her students, discovers a case of severe bullying in her class. When she intervenes and physically disciplines the ringleader, Kurokawa, a boy from a powerful political family, she sets off a chain of terrible events. In retaliation, Kurokawa and his group exploit Sakurai's severe wheat allergy. They trick her into eating a muffin made with wheat flour, causing her to suffer anaphylactic shock while driving. The resulting car accident causes her to lose her unborn child. The students, protected by juvenile law, show no remorse and continue their lives without consequence.

Two years later, Sakurai returns to the same school as a teacher. Now cold and calculating, she confronts the five main perpetrators—Kurokawa, Nishida, Iizuka, Asakura, and Mashima—giving them an ultimatum: confess and turn themselves in to the police before their 18th birthdays, or face her judgment. Each student is a distinct target. Asakura, an aspiring idol, is lured into a sham talent agency and forced into the adult film industry. Nishida, the star of the track team, is framed for doping. Iizuka, the bullied boy who was coerced into delivering the muffin, is psychologically tormented over his guilt. Mashima, a violent and promiscuous student, is stripped of his social standing. Finally, Kurokawa, the arrogant and privileged mastermind, sees his family's political empire systematically destroyed by Sakurai's meticulous planning. The story follows her methodical, psychological, and often cruel revenge, exploring themes of justice, the limitations of the law, and the devastating consequences of unchecked cruelty.