Rena begins sharing a two-family home after her daughter gets married. The family appears happy and close, but she is sexually unsatisfied with her husband and secretly masturbates. One night, her son-in-law Satoru spies on her. When she questions him, he explains that his cock is so large her daughter refuses him. Captivated by his massive erection, Rena tells herself she is only helping the young couple and begins taking care of his sexual needs. Satoru is bewildered at first, but the seductive skills of the mother-in-law who constantly pursues him gradually steal his heart...