Well my GF and I play with this fantasy often. We don't do the cutting of course.

It is medical setting. A girl has been sent to school doctor (or nurse in internet RP) because of masturbation. Doctor tries everything to prevent girl from masturbating again, but he is unsuccessful. So he decides to circumcise her as a final solution. he prepares her for surgery (shaves and cleans her and stuff). That's kinda it. I would never do anything to harm my slave GF, so i can't really cut her. Even then, sex would be less fun, because i like to pinch her clitoris.