Ijôna yubi: Yamete! (1980)

A peaceful morning. A leisurely breakfast scene of an ordinary family: father, mother, eldest daughter, second daughter, and eldest son. A commotion ensues when a man with a gun intrudes. The man begins to reveal the sexual habits of each member of his family, and while holding up a gun, tells them to recreate their sexual habits here. The mother masturbates with a vibrator, the eldest son has incest with his girlfriend's sister, the father secretly films the second daughter's naked body. The man's desire gradually escalates...