I was mainly looking to see if there would be interest in such a transformation, and it looks like there will be. Thanks to all who commented.

RoseyRedd:

There would have to be a legitimate reason for the gender and species transformation. I think an interesting side would be if she maintained minor traits from her feline origin that she had to hide. like cat eyes that need to be hidden by contacts, slightly enlarged canines, or a vestigial tail, hiding pointed or feline ears with hair. tufts of body fur, slight paw padding on the hands. Something that would cause concern and panic about being discovered.

There will be, his transformation will be part of the banishment spell. The one who banishes him will want to humble him so transforming him into what he perceives as a weak human female is a suitable punishment in that person's eyes. I initially toyed with the idea of giving him some lingering feline trait, like eyes or ears, but I'm leaning away from that now. Knowing what I know of his personality, it would give him some excuse to consider himself superior to humans. A large part of the story will involve him struggling with his self-worth.

grim city girl:

Maybe no physical traits rather the nature of the cat eg. hissing at certain things, or attracted to moving objects/stalking.

This is something I've considered. Think on this, if this is a creature that has evolved from a cat rather than a primate how much of the behaviors will it have inherited? Look at chimps, our closest relatives, how many behaviors do we share with them? That's not to say I won't have him mimic some cat-like behaviors, but I don't want to go over the top which tends to happen often when dealing with anthropomorphic animal characters.

Guest Reader:

If he's transformed into an Amazon, or some five foot nothing makes a big difference.

Is his essential personality pretty much the same, or does his body have less brain power or more?

Is this going to be a new person, or is he replacing someone?

It would be neat if he's thrown into a situation where he has to adapt rapidly, but because he's got no background, he's rocked by the situation and unable to handle her normal duties. Say he's now in the body of a counter spy in an essentially Mission Impossible situation, put there at the absolute worst point in time.

Or maybe he's in the body of a super villain right during a battle with a super hero team. He doesn't know how to effectively use her powers and doesn't want to be a villain, so he has to figure out how to lose the fight w/o having the other bad guys against her, and then how to go over to the good guys.

He may also have to have her go from a straight girl to a lesbian or something.

Or maybe he's transferred into a supporting position, like as some super hero's sidekick, which he wouldn't be used to.

There will be no body swap or possession. Truth be told if he did end up in the body of a supervillain and found himself under attack from heroes, he would not hesitate to attack. His viewpoint is very black and white, and if he is under attack he would attack first and ask questions later. Even if he did discover that he had attacked a hero, it's unlikely he would feel remorse. He views humans as inferior and he would see nothing wrong with defending himself even if it meant the death of a hero.

That being said this will be a straight up transformation. There will super powers (through the above mentioned magic sword), but he must get past his self-doubts in order to use them. His mental capacity is the same, but I may have him doubt it due to his prejudices. He will rely on others to protect him and won't even be able to render much aid. He will be very small and weak. His self-value is very much wrapped up in his strength and power as a warrior, so to lose all that will be incredibly devastating. His sexual orientation is not so much a concern for him, as his people do not have any prejudice toward homosexuality or bisexuality, but he views humans as lower life forms. Sexual attraction to a human (which he will experience) will be just as devastating as his loss of prowess.