New Wife's Private Parts: Caress (1991)

This deliriously warped S&M softcore film from cult pinku-eiga director Hisayasu Sato deals with a deranged doctor who lives in an abandoned hospital with his wheelchair-bound sister. The sister has a bizarre disease which keeps her eternally youthful and flawless in her brother's eyes. Frustrated by normal women's perceived imperfections, the madman kidnaps them and submits them to gruesome tortures under the guise of anti-aging experiments.