Oh yes certainly! This sounds like it it would be really fun to play with, so we have nothing against what you've described to us. In general, as long as nothing breaks the game, we have no problems with it. If you ever want to use the planet's interference - either to make Hotaru less capable of holding control or the same for Mistress 9 - then you're welcome to that.

We do ask for just a short section on your app describing anything relevant to Mistress 9 (any differences in powers, if there's an effect on Hotaru aside from just being possessed, something about her personality, that should be enough).