To the Heavens and Hells, Mortal Realm acted as a mirror separating them. The Mortal Realm was also the place where humans worshipped the ones above and below them. Also as the place where Gods and Demons were born.
Mortals who ascended became a God, and mortals who descended either became a Ghost, a Demon, or something different. Gods lived from prayers and worships, as well the virtue of the living. Demons and Ghosts, on the other hand, needed the sins and fears.
The cause of the war between three realms was no other than the significant difference of them.
In the time of war, many great weapons were created. Many legendary swords were forged. And many legends, hero or not, rose into power.
Even after the war had ceased and a peace had made, the reminder of the past still lingered.
The Nine Weapons of Calamity.
The Nine Instruments of Heaven.
The Nine Rulers of Underworld.
The Nine Generals of the Jade Emperor.
Gods create and bless. Demons destroy, devour, and curse. The circle repeated itself, again and again, over the time. Present and future unchanged, just like the past. The gap between the two realms was too big, even the Mortal Realm couldn't bridge the two realms. After a few centuries of war, a pact was sealed.
And the reminders, were passed from generation to generation. Heaven passed the Nine Instruments orderly. While Hell fought for the Nine Weapons.
After sometime, the structure of the underworld changed. Nine Rulers became only one King. The Nine Weapons were lost, taken as treasure, or claimed by another. Although so, the Three Realms are no longer in chaos...
Until.... A fall that changed everything. Not only the banished deity or the boy's life, but all of the Realms. Once more, the safety and peace crumbled into the chasm of disorder.