Lesson of the Evil

Hasumi graduates from Harvard College with an MBA and spends two years at Morgenstern, a European investment bank. He then returns to Japan to pursue high school teaching, bringing with him a polished charm that masks his darker impulses.

Outward charm masks Hasumi's cold, antisocial personality. The narrative notes that he killed his parents and his form tutor at fourteen, foreshadowing the killings to come.

In the United States, Hasumi meets a fellow killer named Dave, and the two form a disturbing partnership. They are depicted carrying buckets of human blood, bones, and organs, hinting at numerous unreported murders.

Hasumi eventually kills Dave by knocking him out and burning him alive inside a barrel, explaining that while Dave enjoyed killing for fun, Hasumi does not.

Back in Japan, Hasumi tackles cheating by secretly jamming cell phones during exams, ensuring a cheating-free test. The move triggers suspicion among teachers and students who notice the abnormal loss of service.

Tsurii, a Physics teacher, becomes suspicious of Hasumi after learning of past student suicides. Hasumi learns of the suspicions by bugging a room, then confronts Tsurii on a train and murders him, making it look like a hanging suicide.

Hasumi confronts Keisuke, the cheating ringleader, tortures him to admit the cheating, and then kills him, preventing exposure.

A female student Miya becomes entangled with Hasumi after being blackmailed by PE teacher Shibahara. Hasumi reassures her of safety and begins a romantic relationship, intensifying his manipulation.

Hasumi uses Miya to access an online private discussion board used by students and anonymously posts claims about the murder of Rina's father. He also blackmails art teacher Kume into lending him his luxury apartment.

After a fight at the school, Hasumi lures delinquent student Tadenuma out for a drink and murders him; the students later believe Tadenuma ran away from home.

During the school's haunted-house event, Hasumi lures Miya to the rooftop, knocks her out, and throws her off to fake her suicide, forging a note to support the lie. Miya survives the fall, keeping the threat alive.

Hasumi stages a mass killing by wearing Kume's shoes to frame him and uses the intercom to warn of an intruder with a shotgun. Students head to the roof while others barricade the art room, creating chaos and fear.

Kakeru, an adept archer, escapes to call the police but returns to rescue Satomi. A confrontation with Hasumi ends with both men firing; Kakeru is slain and Satomi dies.

Two surviving students improvise a cover by disguising two dead peers and hiding inside the school, while tossing the real corpses down an emergency chute to mislead Hasumi. The defibrillator records include an audio clue naming Hasumi as the killer, and the ending shows Miya calling Hasumi's name with 'to be continued'.