Everyone goes on and on on how we should be able break dom this and dom that, but what about building up a sub into your master(gender neutral).
Imagine if you will someone like Ryn -- timid, good natured and without much backbone to her. Now imagine you, through much encouragement and praise, with some dick suckage on the side, you gradually build her and build her into a perfect las that can take charge of your ass.
Hell, you do not need to be it gradual -- just giving a character a taste of how it is to be on top, especially with you as their bottom/service top, would be fine enough of an excuse for them to suddenly switch to a chad thundercock or her pussy-whipping majesty. Better yet if they keep some of their prior demeanour that emerges to the surface from time to time. Whisperings "sorry If I am going to hard to you" before yelling "take it, you bitch!"
My preferably type of NPC would probably be some femboy/twink like Vicky or June. A guy that is shy and insecure about their sexual prowess, but when faced with champion acting all subby and breedable, they slowly turn more and more pusshy untill they literally push you into the mattress and rail you. All the while still acting cutely. And yes, this is my Josou Seme bias talking.
Also, I would prefer them to be small/short. We need more small and compact doms!