You're in the principal's office with your teacher Mrs. Fyre because you were caught grabbing girls' butts in class. She calls in your sister Mandy to help her understand what's going on with you. Mrs. Fyre explains that if this was a public school you'd be expelled for sexual harassment, but at this private school they believe in teaching good behavior as well as academics.

As your teacher asks more questions about your activities at home, it becomes clear what the issue is: Mandy has been teasing you with her ass, showing off in the shower & while she's dressing. Mrs. Fyre reminds Mandy of one of the school's rules: If you're part of the problem, become part of the solution. She's not going to make Mandy do anything she doesn't want to do, but if she doesn't help you, you're going to be expelled.

Mandy really doesn't want to see her brother in trouble, and she knows it's her fault you're in the office. She's at least partially responsible for your ass fetish. Your teacher pulls up Mandy's skirt & encourages her to show off her ass to get you excited, then Mandy rides your cock. Eventually her legs get tired & your teacher agrees to take over for a little while. She's really committed to helping you overcome your sexual frustration so you can be a better student. You're in heaven with two big asses bouncing on your cock. It was totally worth getting in trouble to get this kind of special treatment.