Nanako are close step-sisters. They both got married and left home, but returned to their parents' homes due to their husbands' violence. The sisters are not alone for the first time in a long time, and they reminisce about old times and decide to take a bath together like they used to. Perhaps because she was drunk, Nanako Nanako her older sister Yuu to show her how she masturbates. Yuu is confused, but gradually starts to use her fingers in earnest, and her younger sister, watching, becomes excited...