Hiroka lives happily with her husband, daughter and husband-in-law. But there is one thing she is dissatisfied with in her happy days. She is always frustrated by her husband's sexual encounters, which are much older than her. One day, Hiroka peeks at her son-in-law, Takeshi, masturbating. She loses herself in the sight of his enormous, powerful cock, and can't help but forcefully seduce him. Unable to resist his mother-in-law's blatant and bold advances, Takeshi is swept away and ends up having a relationship with her. And so, regardless of time or place, the two of them continue to make love all the time.