After losing her parents, Momoka leaves high school and raises her younger brother alone. When he unknowingly accepts an illegal job and is threatened by a criminal gang, she accompanies him to apologize. Smitten with her beauty, the leader offers to erase the debt if she serves as his mistress for ten days, and she accepts. His sex is rough, sadistic, and treats her as an object for release, but the alternating cruelty and tenderness—and the degrading way he uses her—gradually awaken her masochistic desires until she submits completely.