The Nine Stars Domain wasn’t far away from the Nine Moons Domain, and there were no boundaries. However, there was a Sea of Death between them. That was the natural boundary between the Nine Stars Domain and the Nine Moons Domain.
The Sea of Death isn’t dangerous at the edge, but it would be exceptionally so once you arrive at the deep ends about tens of thousand miles in. There’s a terrifying island and creatures both in the air and underwater. To pass through the Sea of Death, you’ll need abilities. It is rumored that the dangers here are incomparable to others.