Would be hell to play, though, there's definitely better horny RPGs to try
My issue with horny RPGs is that if you can find people to play with that are into whatever kink the book is catering to, why would you bother to play at all? Just have sex.
And on the flipside, if you dont want to have sex with the people you're playing with, why play the sexy game? Just play a regular RPG
"you feel the spell take hold, but for some reason the crown remains rusty"
Then you pivot that the rust is a powerful illusion or some kind of curse cast on the crown by someone related to that backstory to keep it hidden. Then while your players try to figure out why simply cleaning the rust didn't work, you try to figure out how to weave in that backstory sooner than later.
If you're really not ready for it to happen, make sure they have some other quest to do that has a pressing time limit.