田口ゆかり 裏本番恥技 (1989)

Yukari's life is in despair after the sudden death of her beloved mother and the betrayal of her sister Chidori, who cuckolds her. Yukari tries to commit suicide, but is fortunately saved by Yukio, who runs a guest house nearby. However, Yukari's glamour is too much for Yukio, and he rapes her. Yukari also happens to be having an affair with Yukio's father, Taizo. Yukari is confused by her own sinfulness, but...