Sayuri lives in a two-family home with her daughter and son-in-law, working as a homemaker while occasionally modeling swimwear. One day, she catches her son-in-law Kunio masturbating with a swimsuit she wore. She learns that his enormous cock has caused problems in his marriage, but the sight of it leaves her transfixed. Claiming she is only helping her daughter, Sayuri relentlessly tempts him day and night. After being denied for so long, Kunio can no longer resist her seductive displays.