After a horseback riding accident claims her stallion's life, gym teacher Ritsuko Morita undergoes a bizarre transformation, developing equine genitalia. Initially bewildered, she succumbs to intense pleasure, leading to uncontrollable urges. As her desires escalate, she fixates on her female students, envisioning erotic encounters. Struggling with her impulses, Ritsuko eventually acts on them, crossing a dangerous line with a student one fateful evening.