C574 Mists!

Earth, was also known as the Sixth World, or rather, the entire universe was collectively known as the Sixth World.

Aside from the Netherworld, the other five interfaces did not know of the existence of Earth. Earth didn't know, within the 'big interface' of his life, there were 5 other interfaces as well as the existence of the Netherworld.

Earth's humans only knew about the universe