First, let me say that I really hate doing this. The story I'm going to offer is actually one that I had started with another author, but for personal reasons it looks like he will be unable to continue, at least any time soon. However, it seems to me that a good story is a terrible thing to waste, and so I'd like to put it back out there.
It takes place on an alternate version of earth, in the not-too-distant future (mst3k reference, anyone?). I'm going to say maybe 30 to 40 years from now. On this earth, humans managed to evolve a third gender, officially called "intermale", although there are a few slang terms. They are essentially female, except for possessing male sexual organs. They're also, generally, taller, somewhat more muscular (they're not body builder-type, just a little bit physically bigger) and usually with larger breasts than normal women. Their penises, as well, tend to be larger on average than male's.
Throughout history, intermales have been used for slavery of various types, but often of a sexual nature. During the time of our story, they are bought and sold on open markets, from facilities specifically designed and built to raise them from birth to the age of eighteen, training them in all sorts of domestic skills and sexual practices.
My character is Candice, an intermale who has just come of age and is ready to be sold. She is rather special, though. She stands just over six feet tall, which is impressive even for an intermale. Her breasts are quite large; double-Ds at least, and her penis, when erect, measures nearly a foot in length. The facility has already tried to sell her once, asking a remarkable price, but was unsuccessful. Candice isn't always willing to do exactly as she's told, and none of the buyers really wanted to spend that kind of money on an intermale, regardless of her physical characteristics, if they couldn't control her.
So, after a few days, she's placed on the market again, this time steeply discounted. That is where your character comes in. (I'll assume "he" for now but it really doesn't matter). This is his first, reluctant, purchase. He goes in not knowing how much intermales really cost, and is discouraged by the prices, until Candice shows up. Not only is she remarkably inexpensive, but something about her size... all of her sizes... is appealing. He purchases her without a thought and we go from there.
As I said, I had started this story with someone else and we got to the point where he gets her home and they have more or less worked out the type of relationship and sexual things they will have. It was being played where he was going to be somewhat more of the sub, sexually, and pretty much wanted her to be the sexual "top". I'd kind of like to keep this feel, and if you decide you're interested and would like to read the story I have so far, let me know.
Fair warning: I do expect male characters to perform oral sex on her and to allow penetration.
This story is open to anyone, and your character can be either gender, although it does seem to work better with a male character. If you are playing across your natural gender, I would ask that you have some experience doing that, as the gender roles in this story are already skewed.
PM me if interested.
Thanks for looking,