Nao, the younger sister who lived an otaku life in the countryside, moved to Tokyo after graduating from university. With no job or room to stay, she decides to stay with her older sister and her husband until she can find someone to help her. However, Nao is shocked by how crazy her sister and her husband's nighttime activities are. She peeks at her sister's intense thrusts that seem to break her, her screaming moans, and her body arching back as she climaxes over and over again, and her crotch gets wet. Unable to stop her overflowing desire, she takes bold action...