Amatsu-Mikaboshi is a being that is unnatural yet natural because it was made from the remnants of the inverse energy of the Goddess Izanami. The Shinto group of gods in the eastern continent are not from this world as they came from a universe outside of it. They are gods that actually came from a universe that was ruled by another powerful being. Amatsu-Mikaboshi was not born when the Goddess Izanami came forth as she did not possess a shadow when she was in her original universe.
In fact, all of the Shinto gods did not possess a shadow as they were different compared to the gods of this universe. They did not possess shadows because they were born as pure beings that cannot be tainted. They were beings of Order which is why they are vastly different from the Gods of Pandemonium. They were born from the parts of Order when Chaos clashed with the former.
