Taella-Oso and Taella-Bruha

The Beginning
The lore book "The Book of Y'llah" contains the story about how Taella-Oso and the sister realm Taella-Bruha were created by the gods Ma'at and Ba'al:

In the beginning there was only the void. But the goddess M’aat and her brother B’aal looked upon the void, and they knew that it should not be thus.

M’aat, who knew the names of all things, spoke into the void. Her voice echoed through a new world, giving it order and filling it with light and truth. The land and the sea; all the creatures in them, and all the stars in the sky. She created all these things, and she created man. She saw what she had made and she knew that it was good.

Her brother, B’aal, also knew the names of all things. But when he spoke, his voice created a world filled with chaos. He created a world filled with horrible creatures, imps and golems and dragons. It was a world of eternal darkness. M’aat saw what her brother had wrought, and she knew that it was evil. She sealed it away, placing a veil between her realm of order and his realm of chaos, so that her creation could dwell in the light and not the dark.

And so it was that the realm of man was shielded from these dark and terrible things.