What exactly IS necrozma? We know it’s some dragon that eats light that got banished(?) to our dimension and it became weakened and corrupted(?) (because it’s body as introduced in SM is all mangled and warped?)

But what is it’s place within the pokemon lore and legendary hierarchy? Now that I think about it, what about eternatus?

Surely pokemon hasn’t devolved to the point where they just introduce abstract powerful beings and give them no context in the franchise, r-right?