The Demon Realm: eternal enemy of Heaven.
Of the three realms, the Demon Realm was unique in that its Realm Will didn't follow Yuanqi's orders—acknowledging only one master: its beloved creator, Huan Yi.
In the middle, late, and final stages of the Primordial Era, the Demon Realm ruled supreme, dominating the Celestial Realm effortlessly. This couldn't be helped. With the strongest of all Incarnations leading them, how could the demons not lord over the gods and immortals of Heaven?
But in the billions of years that followed the Demon Child's imprisonment, the Demon Realm underwent drastic changes. Fraudulent Demon Monarchs succeeded one another—failing to unite the tribes or subdue the Devils to lead the Demon Realm back to the peak.
The Celestial Realm, on the other end, kept getting stronger, eventually causing Heaven to surpass the Demon's Will.