Ryoko and Ayumi are close step-sisters. They both got married and left home, but then got divorced and returned to their parents' homes. One day, the sisters were drinking together and reminiscing about old times when Ayumi invited them to take a bath together like they used to. Perhaps because she was drunk, the younger sister asked her older sister to show her how she masturbated. The older sister was hesitant, but gradually she started using her fingers in earnest, and the younger sister, watching, became excited...