Kanade returns to his rural family home for the first time in years. His sister-in-law Sarara is still the same modest, gentle woman who faithfully supports his older brother—the perfect wife. But on a sweltering summer night, Kanade catches her drenched in sweat and lost in pleasure as she masturbates in a room with a broken air conditioner. Beneath that respectable exterior, Sarara is a depraved temptress who cannot control her urges. After being caught in the middle of her filthy masturbation session, she seduces her younger brother-in-law while her husband sleeps only feet away and greedily goes after his young cock. That night begins a forbidden affair neither of them can ever reveal.