Fubuki Haneoka, a naive yet fiercely loyal male student, dedicates himself to aiding others despite occasional jealousy. His resolve centers on protecting his stepsister Miku, whose deteriorating health stems from her involvement with a school gymnastics team. Though unrelated by blood, Fubuki employs unconventional tactics rooted in adult-oriented narratives to rescue her.

Tomomi, a pivotal manipulator, coerces him into coaching "Dark Gymnastics," a deceptive scheme promising Miku’s recovery. To infiltrate the all-female gymnastics club, Fubuki adopts a female disguise. Within the team, he partners with Koyuki, a recruit ensnared in Tomomi’s orchestrated explicit scenarios.

Across official media, Fubuki navigates the morally ambiguous world of the gymnastics team while training Koyuki as a Dark Gymnast. His actions are driven by dual forces—obligation to Miku and the repercussions of Tomomi’s schemes. The narrative examines non-biological familial bonds and the psychological strain of his decisions on interpersonal relationships.