Seventeen-year-old Kaoru Sugimura has a sadomasochism fetish. His greatest joy in life is learning different types of erotic knots and maintaining his gear. Unfortunately, he lacks a partner to try all of the items in his collection.

Kaoru's ideal playmate is his childhood friend Nana Chigusa—the beautiful and popular vice-president of his school's student council. However, their relationship has worsened over the years because of their conflicting personalities. Kaoru neglects his studies in favor of his deviancy, while Nana is constantly stressed due to her focus on schoolwork.

Disappointed by Kaoru's study habits and erotic hobbies, his mother secretly gives Nana some of his S&M toys for safekeeping. Intrigued by the leather costume, Nana tries it on, only to end up accidentally locking herself in. After Kaoru frees her, she realizes that S&M helps her relax and, much to Kaoru's delight, asks to engage in more erotic stimulation sessions.