Jun is a high school student who enters a secret romantic relationship with his teacher, Katsuko Kurose. Their relationship, built on mutual affection, culminates in Katsuko giving Jun her virginity as a birthday gift.

Their secret is discovered by Jun's classmate, Kazuya Shinohara, who witnesses an intimate moment between them in a school classroom. Kazuya uses this knowledge to blackmail Katsuko into having sex with him, threatening to expose the student-teacher relationship to the school authorities.

Jun remains unaware of the blackmail for some time but eventually stumbles upon Katsuko and Kazuya engaged in a sexual encounter. Hearing Katsuko make statements about enjoying Kazuya's advances and begging to be impregnated, Jun becomes heartbroken and angry. He breaks off all contact with Katsuko, convinced she willingly cheated on him.

After graduating, Jun has a chance encounter with Katsuko three years later. She confesses that Kazuya had been blackmailing and raping her throughout their school days to protect Jun from expulsion. Despite this revelation and Katsuko's declaration of enduring love, Jun finds their subsequent sexual encounter emotionally unsatisfying. He observes that her behavior and sexual techniques have changed, believing she learned them from Kazuya. Concluding that he cannot rebuild trust after the past lies and deceptions, he rejects a renewed relationship with her. This final rejection leaves Katsuko emotionally devastated.

Later, Jun is visited at his home by Katsuko and another woman named Miki. Miki, revealed to be another victim of Kazuya's manipulation, has just murdered him. They visit to help resolve the situation between Jun and Katsuko, though the outcome of this interaction is not fully detailed.