In the Primordial Epoch, before the Immortal Realm, the Demon Realm, and the Demon Realm came into existence, there was only one world, collectively known as the Mortal Realm.
In this era, mortals and demons lived together, often suffering from oppression and slaughter by demons, with constant warfare on the human lands, and no order to speak of.
It wasn't until a peerless hero emerged that he led the Human Race to resist the demons, repeatedly crushing the demon armies and forcing them to retreat to their own territories, and from then on, humans had a place to survive.
To celebrate the great achievements of this peerless hero, people honored him as the emperor of the Human Race.
The Human Emperor knew that the Human Race needed to establish a complete system and unite as one in order to have the strength to resist foreign races, so he assumed the responsibility without hesitation.
