I'd have a fun idea in my head for a while. Where the main character being a warrior from one of the Keidran races, tigers,wolves, leopards, etc etc. As he would be going deep into human lands, one of the few of his kind to get in there once the trade relations between the two races has gone up and allowing the mixing in the first place.
The trick being that this individual would have a special curse, where when he has sex and inseminates a human girl with his seed, she will turn into a random Keidran of the races. He can then alter this trait of his to also change the girls mind, either allowing her to keep her self conscious, or turn into a wild unintelligent kitty, and everything in between.
So his goal is to travel the human lands and change as many human girls into his race as possible. All the while trying to not get caught along the way.