There is a secret competition known as "dark rhythmic gymnastics." The entries demonstrate their beauty and lewdness through techniques that are more difficult than those in standard rhythmic gymnastics. Haneoka Fubuki is the younger brother-in-law of Haneoka Miku, who has gone missing. While searching for his sister, he finds her at the home of Tomomi, Miku's classmate. According to Tomomi, she is trapped in the dark side of "dark rhythmic gymnastics." To help her escape, he resolves to become a coach of "dark rhythmic gymnastics" and gets close to Fujimiya Koyuki, who was chosen by Tomomi without knowing her fate...