A woman who was turned into a human toilet: Slave Castle Gaiden

Mariko (Hazuki), the only daughter of a wealthy wealthy family, is caught by Chie (Kobayakawa) looking for a woman who will become a human toilet after receiving a request from a sadistic, casual lady. She is kidnapped and imprisoned by Chie's plan, who has infiltrated as a servant, raped by a masked man, and is forced to serve as a lesbian while being trained to a human toilet...