Aliens, robots, Biblical creatures disguised as a cute girl transfers into [protagonist] school is a cliche.
But, how do I really do it?
Local skin tone, Accent, Mid-class and other average student physical characteristics. The being has sufficient common sense and mental health to not look out of the ordinary.
But, has no, ID card, birth certificate , basically in the eyes of the government doesn't exist. Like just pop out of nowhere. Like a bastard born child kept quiet or something.
How to solve this assuming mind-control and all manner of magic is out of the question. Actually does not have to be a super-natural in the first place.