Mei Kamisaka discovers her mother's hidden sexual desires, making her realize she has masochistic tendencies. She secretly spies on her stepfather and mother's BDSM sex, captivated by the sight of her mother bound, which sparks her own interest in bondage. That night, while her mother is away, she sneaks into her stepfather's room to peek, gets caught, scolded, and punished. From then on, the training intensifies, and she gradually descends into becoming a rope slave.