With his marriage long since gone cold, Ozawa finds his only comfort in teaching. During his final year before retirement, one adult student begins to unsettle him: Hikari Azusa, the serious, high-achieving student council president whose grades have mysteriously slipped only in his class. He arranges private tutoring after school, but Hikari ignores the lesson and simply watches him with a knowing smile. When he tries to reprimand her, she suddenly kisses him, and from that day their forbidden adult teacher-student role-play grows increasingly intimate.