One day, Akari was found abandoned on the street and taken in by a perverted older man who began keeping her as a pet. Forced to wear cat ears, a collar, a duck gag, and even an anal tail, her body gradually begins to change. Subjected to harsh training sessions involving foreign object insertion, enemas, and anal sex, Akari—who had no prior anal experience—slowly finds her anus stretching wider and wider. Shocked by her own transformation, she begins a new life embracing her altered state.