The bond between sisters who lost their parents transcends mere affection, transforming into deep, overwhelming desire. Between elder sister Sumire and younger sister Riona Minami, there exists a connection stronger than blood. Crossing beyond everyday tenderness, they step into forbidden territory. As Riona sleeps on the sofa, Sumire performs piss drinking lesbian acts on her. "I know this is wrong... but... I still love my big sister," she confesses, unable to suppress her feelings. Love for her sister and her own carnal desires intertwine, pushing them beyond the limits of taboo. Their relationship—sharing hearts, bodies, and bodily fluids—reveals the essence of forbidden love. A series of events where love, lust, and impulse collide not only deepens their sisterly bond but also creates new boundaries.