Betrayed by her trusted boyfriend, Yuna breaks her pre-marital chastity and asks Junghoon to have sex with her. Junghoon then tells this to Yena, Yuna's younger sister and friend, but Yena's expression is somehow not good. Junghoon has an unrequited crush on Yuna, her older sister. Yena, in turn, has an unrequited crush on Junghoon. 'Why isn't it me, but my sister? I... I liked him first, so just keep doing it.' This is a somewhat very erotic story of these individuals, each with their own 'circumstances,' as they overcome unrequited love.