Kankin itazura: Himei no aegi (2000)

Nobuko is soliciting donations all alone on a street corner. Sumie, a masturbation enthusiast obsessed with questions like "Why aren't humans born from eggs?" and "Why do we have sex?", has her devotees—Doberman and Husky—abduct and imprison Nobuko. Confined in a cage, Nobuko is subjected to their sexual abuse. Sumie’s older sister, Yuka, lives upstairs; even when she becomes aware of their activities, she dismisses it as just another one of her sister's kinky games and pays it no mind. Then, one night, Husky returns home alone only to be seduced by Catherine—a woman who looks exactly like Nobuko...