Kira finds himself caught in a provocative tug-of-war between his obsessively doting sister, Sarasa, and his sporty junior admirer, Kasuri. After a secret encounter where Kasuri gives her virginity to Kira, a jealous Sarasa attempts to reclaim her brother's loyalty through a risky tryst in a restaurant restroom. Despite Sarasa's efforts to dominate him, Kira continues his illicit affair with Kasuri, fueling Sarasa's determination to erase her rival from his mind.