Nami Matsukawa's Tied Crazy Flower Core (1982)

On a stormy night, two couples are having a lively SM conversation at a literature professor's mansion. Late at night, Nami was visiting her professor's house when she was invited by the professor's daughter, Aya, and felt her lewd blood writhing inside her body. Aya, who says that she is a virgin, approaches Nami with her S play and forcibly asks her to have lesbian play. Nami's masochist instinct is awakening...