Rina, a high school teacher married for five years, presents a picture of happiness but is secretly unhappy with her sex life and desires solitude. Her sister, Aki, introduces her fiancé, Sumio, a student whom Rina has previously propositioned in an empty classroom. Despite Rina's attempts to avoid him, Sumio persists, pursuing physical intimacy and seeking a rekindling of their past relationship. While Rina is away from her husband, she becomes increasingly consumed by her sister's fiancé, transforming into a sexually driven person.