Chihiro lives with her husband, who works at a prestigious company, her brother-in-law Kojiro, and their parents. On a sweltering summer night, the air conditioner breaks down, leaving Chihiro drenched in sweat as she struggles to sleep. Quietly watching her from the shadows is Kojiro, who has failed to land a job and constantly feels inferior compared to his successful older brother. Overwhelmed by daily frustration, his suppressed lust for his sister-in-law Chihiro finally erupts. Seizing the chance when her husband is away on a business trip, Kojiro sneaks into her room and takes her. The two engage in intense, sweat-soaked sex as Kojiro loses himself completely to uncontrollable desire, betraying his brother and crossing the line of family loyalty.