Of course, there is another kind of existence, they passively learn about the Boundary Sea.
For instance, the Bee Demon Queen Feng Bai Hua, the Black Flood dragon, and the Five Great Sea Demon Kings that Ning Qi subdued in the War Domain.
These Boundary Sea Beasts were not born in the Boundary Sea initially; many were exiled by the world.
It's not that they committed some great crime, but the World Will and the Ancestors need them to explore the Boundary Sea on their behalf.
For instance, realms like the Mountain and Sea Realm and the Vast Realm, their Spirit Realm Will cannot leave the world yet needs information about the Boundary Sea, so they must send out some Demon Beasts.
As for why they are not humans, Demon Beasts are generally more adaptable, with thicker skin.
And humans, there were indeed some Spirit Realms that attempted to exile them too, but the results were bizarre.
