Girl and the Wooden Horse Torture (1982)

Nami is a masochistic high school student who is attacked and almost raped by a gang of hoodlums before being rescued by handsome teacher Muraki. The near-miss triggers bizarre hallucinations in Nami, and she imagines herself engaged in various S&M situations with Muraki, in which she is beaten, forced to urinate, and tortured on the titular wooden horse. The hallucinations grow progressively more real (and exciting) to Nami, and soon Muraki is accused of raping her and loses his teaching position.