Teacher's Pet (anime)

Teacher's Pet (ナチュラル) is a hentai anime about a student, Chitose, and her professor, Haruhiko, whom she loves and with whom she has a sexual relationship. However, there are certain circumstances that put their relationship in jeopardy, such as Haruhiko being the ex-boyfriend of Chitose's older sister, and Haruhiko being old enough to be Chitose's father. Tension begins to arise when Haruhiko begins to fall for a fellow teacher at school.