Hakubinyû Hisho: Inbi Na Nama Ashi (1998)

A voluptuous secretary is an orphan and instead has been raised by a guardian. The guardian demanded sex in return. He came to her office one day to ask her if she could help his son be hired. The secretary and son develop feelings for one another. The father finds out, is angry and disciplines her physically. The son comes to realize that his father and the secretary are sexually active.