After reading that sex feels incredible following a month of abstinence, his girlfriend makes him quit masturbating. From that same day, her adult sister Mito starts tempting him. He normally brushes her off, but pent-up lust makes it impossible to ignore every flash of panties and cleavage. With only one day left, she whispers that it is not cheating if he wears a condom. His restraint collapses, and he pounds her slender body until the entire box is gone. Even that cannot satisfy the desire he has stored up, so they move on to forbidden raw sex and repeated creampies.