I have to agree with ktc. This feels like an excerpt from a full story. This is good, but would be even better with the events leading up to it.
I feel like you cut out a sex scene in a story you wrote. I'd be interested if you developed the mistress' character more, where did her powers come from perhaps? Just feels like it could be a full blown erotica and instead its just another shem story. I feel like I'm overly critical of everyone here, but I did enjoy the story for what its worth as there was boobs and there was sex.
I personally would like a background story of the mistress. Was she a normal, every day girl once? How long has it been since she was turned into a vampire (or he)? Can she control whether they turn into a succubus? Just giving some ideas because I think its a good direction. The only thing problematic with your writing was the lack of character development.
For example, BB47's recent "A Christmas Wish", which I'm using because its the most recent and accessible story, while a fairly typical "Guy meets girl who also loves BE and girl grows boobs by magical/chem/alien which leads to awesome sex",is a pretty rehashed progression of events, was still filled with the main male not being a total Mary Sue in that he had a stutter and had a regular life outside of his work, which added to some amusing humor thrown in when he was asked to be Santa, and later when Mindy comments that he can still talk after watching her grow boobs and then suck him off.
Even taking into account that Mindy in this story is just every readers dream girl, its still a personality and character that you can semi-relate to. Your characters are just objects in the sex. There is no quirky stutter, so to speak.
Sorry for the long ass comment, but just because its porn doesn't make it not good writing and yours has potential to be more than just another sex story.
Good- wish it was longer
That was rather good.