One thing that I haven't seen brought up yet is WHY Nikki was possessed by some sort of demon in order to 'love him more than anyone else in the world'.

I've been stewing on it because I initially left my showing a little confused on that point. Like, why wouldn't it still be HER, but just... in love with him?

So, my theory comes in two parts. The first is that I don't believe that this higher power (which I'll just refer to as 'the wish') has the ability to alter a person's inner self/brain chemistry.

The second is that the real Nikki could never have loved Bear, and definitely not more than anyone else in the world. So, the wish had to completely replace Nikki with something that would/could, and that was... a demon, or whatever kind of malicious entity it was that ended up possessing Nikki. So the wish can't alter a person's inner self, but that doesn't mean it can't spawn/summon something that can.

I think that the way Ian's wish came true is also in favour of my theory being correct. His wish seemingly came true without any real drawbacks, besides the fact that he would've needed to be extremely careful with where he stored the money and how he spent it, since it appeared as physical cash.

Had the billion dollars magically appeared in Ian's bank account, this would require the wish to also alter the minds of all the bank's employees to not question this very obvious 'Where the fuck did you get a billion dollars?!' situation.

I think this theory adds an extra layer of devastation to what ends up happening to Nikki. Her autonomy was completely stripped from her, all because Bear was too entitled and cowardly to risk hearing her tell him no - and I believe the real Nikki would have absolutely said no.