There's a story on Writing.com called Swap Princess, that has a similar plot twist. But it's more of a Mediterranean nation that a fantasy realm. Maybe you should make this an interactive story? Where someone writes one chapter and the next person contributes. As long as you carefully pruned the chapters, it might go in a direction to your liking.
Oh, maybe a Demon Maid or Demon Chamberlain, to help the Princess run things.
(The official Demon Maid uniform -- maid tiara thing, long latex gloves (to the elbows or further) with little bows around the wrists, long latex stockings, a pair of latex bows on the girl's tail -- a big one at the base (so it frames the butt) and a small one at the end, and a half apron whose strings go up the maid's cleavage, forming a collar around the maid's neck, and which doesn't quite go down far enough to be useful for much of anything.)
Oh oh oh, yeah -- the poor Princesses' best friend (or perhaps girlfriend) from Earth, pulled down when the Princess makes an offhand comment about missing them and needing an assistant.
Could play that up either way, maybe both at the same time:
Best Friend (Male -> Satyri Maid)
"Dude... I know this sucked, but... did you HAVE to wish for me to come help?"
"Hey man, you always said you wanted to get your hands on a nice pair of jugs."
"Yeah, but not my OWN!"
Girlfriend (Female -> Succubi Chamberlain)
"Honey... It IS you, isn't it?"
"That's what I've been trying to tell you!"
"I... I can smell your essence... it's really you under there..."
"Honey... your soul... it smells..."
"... DELICIOUS ..."
Or maybe his little sister, who is just a little spitfire, a holy terror running around causing more trouble than the demons.
"Sis, Sis, stop, stop, NO, BAD, I've told you a thousand times, Don't Bother the Succubi!"
"But I was just going to put Wasabi in their Bath Oils again!"
"Ok, I admit it, that was kinda funn... NO, BAD, Get back here!!!"
"I... i can send minions to pillage game stores to get my new games, right? right? if we send succubi, they won't have to pay AND they'll get to harvest, like, at least a dozen souls each per new release..."
"........Please tell me this dimension can provide my toys with delicious alternating current?"