I don't think this is the way to do it. The orc in your tale is unremarkable from other orcs. The elf stands out by wanting to be raped and conquered unlike other elves. The disbelief comes from the orc side of things methinks.
Change the orc? He still needs to be a warring chieftain who propagates his species in another species' females. The kink is overwhelming the girl so he can be a cunning foe but in addendum to strength. I really don't know how to make this work with an elfqueen throwing herself prostrate to the rapist. Breaking her maybe, melting defiance is always fun, but you said she's attracted to the monster and becomes his mistress. Mistress's a few levels up from war trophy.
No, this is outside of my bailiwick. If I did orcs and elves, I'd go backwards. The orcs are getting genocided by the sick of being raped elves. The last surviving orc clan is lead by a grand chieftain and his pack of powerful sons and one runt. The strong live to fight, the runt runs to live. The daughter of the queen, against better judgment, gives chase. Something gives runt the upper hand. He's the last, with one slave, one chip that he uses with all of the cunning he needed to survive his brutish brothers hazing to take the queen herself, until to save her species she joins the runt and enslaves her entire people. Making her do it for joy by the end of the book would be more fun than submission for duty.
In conclusion, your idea, as is, is unbelievable and bland. I'd recommend killing the final boss and new game plusing another attempt at life.