Fire Emblem, Tibarn/Reyson with powerplay/BDSM. I'd really love to see the hints we get in canon (it is, after all, textual that Tibarn tied Reyson to his bed to keep him from fighting, whether you ascribe a sexual meaning to that or not) expanded upon. Extra bonus points if it's lifestyle D/s, but if you're not comfortable writing that then keeping it to the bedroom is fine with me, too.