>>29907762The cover trio are based on the three goals of alchemy (transmutation of metal, creation of life, and discovery of the 5th element), which were tied symbolic to the sun, moon, and aether, respectively. It pops up a few other places in the game too, like Type: Null and the Aether Foundation. (supposedly the Ultra Beasts can be tied to the cycle of rebirth, too)
It's just a neat recurring theme in the generation. There's really no meaning to it beyond that.
