I recently thought of something, though you may want to save this for the inevitable review. Considering it’s propensity for “absorbing all the light in the universe” and basically being the ends of said universes, is it possible that Necrozma is Pokémon’s equivalent to the phenomenon astrophysicists call the “heat death of the universe?” That being entropy inevitable cooling down every single particle in the universe until there isn’t a bit of useable light or energy left and everything decays until there’s nothing left so that there’s basically nothing left except complete darkness?
I will indeed talk more about Necrozma when I get to the review, but I don’t know that this works with the way it’s portrayed in Ultra Smoon, or for that matter in the anime. Necrozma used to be a being of light, a creative and generative force. Its dark form that steals light is a result of some kind of damage it suffered in the past, but that damage is supposed to be fixable, resulting in the restoration of the radiant form we know as Ultra Necrozma (which sort of clashes with the feeling of inevitability that the whole “heat death”/entropy theme would be trying to evoke).