After her mother-in-law passed away, the Hatano couple started living together with her father-in-law. Since their marriage, Yui, the wife, has always played the role of a submissive woman who serves her husband to satisfy his desires. However, one day while taking care of her father-in-law, she accidentally sees his erect penis. Seeing her father-in-law getting an erection even though he can't move properly, something inside Yui snaps...