Minami lives happily with her beloved husband and daughter-in-law, but she hasn't had sex in a while and has gotten into the habit of masturbating every night. The same goes for her son-in-law Tsuyoshi, who spends his days spying on her and satisfying himself. Kokoro by his big cock, Minami continues to Kokoro and seduce him at every opportunity. The son-in-law is unable to resist his mother-in-law's advances, and before they know it, the two are devouring pleasure day and night...