Haruto is a high school student, living together with his older sister, Kazumi, and younger sister, Megumi. Kazumi is his classroom teacher and he loves her. One day, he tells Kazumi that he loves her, but she refuses it. He is so depressed and comes back home. Megumi consoles him and they sleep together at last.... Kazumi accidentally sees them having sex and she is shocked to know the fact.... A few days later, when Kazumi masturbates in her room, Haruto sees it and they have sex.... Thus, a battle for Haruto breaks out! No one knows what will happen to them in the end...?