The man who lived with her was thinking about getting married. She also had a good relationship with her younger sister, Urara. One day, a sudden heavy rain caused the trains to stop, and Urara, who was stranded at work and unable to return home, arrived alone, soaking wet. She was also stranded at her workplace and unable to return home, so she ended up alone with her step-sister. When he invited her in, Urara was completely soaked and her underwear was visible, and he felt a sexiness that he didn't normally feel, and he lost his reason and ended up kissing her...