In the history of the Three Realms as Youchan knew it...
In ancient times, everything had originated in the Primordial Land. The word "demon" referred to the myriad spirits of heaven and earth that embarked on the Path of Cultivation, encompassing almost everything under that collective name. Before humanity was born, the Primordial Land belonged to the Myriad Races and Spirits.
And the Celestial Palace was the oldest Dao tradition.
The Lord of the Celestial Palace was the first and oldest Heavenly Emperor, ruling over the many Immortals and Gods of the Nine Heavens and Ten Lands. In terms of standing, even the present Orthodox Leaders of the various Dao traditions fell short of him.
The Celestial Palace itself had become the Solar Star, situated above the nine heavens of the Primordial Land. Together with the Moon Palace, which had become the Lunar Star, it governed day and night.
But rise and decline were the natural order. Over countless ages, as the Three Realms expanded and evolved, the Primordial Land grew ever smaller. After humanity became the dominant force in Ancient Times, it too left the Primordial Land. Only the Demon Race remained in that half-abandoned place, and so the Primordial Land became the Demon Realm.
Then came the Primordial Cataclysm, when the Outer Path invaded.
Youchan still remembered guarding the Well of Primordial Beginning during the Primordial Cataclysm, exterminating every member of the Demon Race. Sensing disaster, the Demon Celestial Palace had tried to leave the Demon Realm. She had attempted to stop it, but the Primordial Heavenly Emperor had driven her back with a single move. He was every bit the equal of those few leaders of the Dao traditions.
Afterward, the mighty beings had retreated to the Heavenly Realm, even moving the Netherworld and Jianmu there.
But