Mmm, that's lovely, that is. The taboo nature of the charm, the public nature of the wank (even though he's 'concealed'). Very hot indeed!
I have to admit that I do feel a bit bemused by the extensive A/N at the end, though - particularly as you talk about issues (breeding, rape) that aren't relevant to your fic. While I'm sure you just wrote it because you felt you needed to cover your back, it does give the impression (to me at least) that you felt bad about the incest fantasy in your fic, and that makes me feel a bit uncomfortable, and takes away some of my enjoyment of your fic. I hesitated to leave this comment, but I hope you'll take it in the spirit it's meant - completely non-wanky and just something to consider for the next time :) I think your warnings in the header were fine, and you could've just written 'This is a fantasy. I do not condone incest in RL' in the A/N in the header if you felt the need.