The great gods devoured the lesser gods, eventually leading to the ultimate confrontation between several mighty Human Gods. In the final, ultimate battle, humans had all but died out, leaving only gods in the world, and specifically, a few powerful Human Gods.
Therefore, that ultimate battle was unrecorded by anyone; it is only known that eventually, the world's atmosphere finally ran out of its source. The creatures born from the Source River also died out one after another. Even the ancient creatures of the Source River, such as those behemoths, could not avoid calamity; only a small number of species were preserved.
So, when I learned that Scouring Sky was still alive in this world, my first reaction was shock because in principle, Scouring Sky should have fallen after the Twilight of the Gods, with only Leviathan managing to cling to life in the deep sea reaches of the Source River.