Iori, his wife's adult younger sister, runs away from home after fighting with her husband and comes to stay with the couple. He sees her as family, but Iori seems jealous of their loving marriage and suddenly starts wearing revealing clothes that emphasize her enormous breasts. She even appears to shake them deliberately whenever he is around. He ignores the teasing at first, but the relentless sight of those bouncing L-cup tits gradually destroys his self-control.