Between brother and sister exists a blood bond, yet their relationship is complex and deep, sometimes crossing boundaries. [Noa] After the younger brother starts living alone as a university student, his sister visits frequently, helping with housework and cooking. Caring and attentive, she discovers a tissue used for masturbation while cleaning—and from that moment on, begins using sex to satisfy her own desires, teaching him sexual acts. [Sakura] A sister who deeply cares for her younger brother, always nurturing and protective. After a date ends and the brother is about to sleep, he receives a message from her—she missed the last train and is coming over. His heart races at this sudden reunion. [Noa] These siblings, who once had frequent sex back home, find their relationship cooling after moving apart—until the sister suddenly returns from the countryside, saying she missed him. Just like in the old days, she overwhelms him with her strong libido, drawing him back into her body. In the end, love and lust intertwine between them, emotions tangled, yet ultimately bound by blood—unable to escape their forbidden connection.