I'm very interested in a specific story line, something M/s but with a little twist.
YC and MC are involved in a M/s relationship. Both are willing, and they have been together for a couple of years. YC obviously calls the shots; everything from the relationship to the M/s aspect of it have been his ideas. MC doesn't realize the staggering amount of subtle manipulation YC uses on a daily basis, things like encouraging her to separate from her family and friends, leaving YC her only friend and confidant. Perhaps even the reason he wanted a relationship with her in the first place was manipulative, maybe she unknowingly wronged him in another aspect of their life, maybe he hates her brother or sister and to get back at them he's wrangled her into a relationship. MC would be almost completely oblivious, and it would almost have an aspect of Stockholm Syndrome, except that she doesn't realize that he's holding her captive.
I'd like the goal of this RP to see how far YC can push MC. He is constantly pushing her boundaries, telling her that as his slave he wants her constantly naked, now he wants her to get piercings or a branding symbolizing their relationship, she should quit her job, he makes enough money to support the both of them and it would please him so much to have her home, cleaning and cooking all day! Maybe one day deciding he wants to start trying to get pregnant without talking to her about it before hand, he'd be ever so pleased if she would let him piss on her, you know what would be so sexy, if she fucked the dog! If she puts up any protest, que the manipulation! "Well honey, I understand it's not what you want and that you're upset, why don't you take the weekend and go stay with Sharon until we've figured it out? Oh? You don't talk to Sharon any more? Well, who do you talk to? You don't have anybody? That's awful, I didn't realize! I guess you're stuck here then, with me." Maybe he ignores her because 'they need some space', making her realize that she really is alone.
In essence, MC is completely and totally in love, head over heels in fact, with YC. YC isn't in love with her per se, maybe he even doesn't like her at all. He just wants to see how far he can push her today, all while keeping up that guise of being in a loving relationship. At least she's a good lay, right?