I read this a few years ago, the main character is this girl that has just enrolled into a boarding magic school, but before even taking any classes she meets this other girl that has God-like powers and a distorted sense of what friendship means (unknown to the MC at this point).

I'm unsure of the order but what happens next is that the MC says she will be her friend which makes the other girl reduce her size to that of a doll, because that's what her other "friends" are. Later on the MC meets some of the other "friends", which are dolls (one of which has cat ears) and plushies turned to life.

And that's as much as I remember, I already tried searching some tags in MU but nothing came up, hopefully someone here remembers it.

Haikou Dolls ?

That's it, thanks!