Demons or demonic beings have varied forms yet unlike what one might think, they are well organized according to bloodline.
They worship the demonic god and take orders from the demon emperor and his seventy two demon pillars.
Demons are also erratic and irrational at times and geniuses at other times, the opposite of their counterparts the devils who are a highly logical species and if not for their greedy,arrogant and prideful personality, they'd be the best option to work with.
And that's why , ten years after the start of the expansion, demons were allowed to roam and make deals with humans and other species using the Jing system.
This was a system created by our mothers and father, using our understanding of runes,the heavenly dao and arrays,a system was created that would allow agreements on a high level to take place using the heavenly dao as an unbiased judge, runes as language and arrays as communication to the heavens.
This allowed deals between even spirits and humans as breaking the agreement can at times equal death and soul destruction.
Due to this monumental achievement we even received the blessings of the heavenly dao,of course this was kept secret.
Demons unlike devils didn't like playing with their words hence their deal were almost always a done deal making them more preferred increasing their influence on the lower planes and in return, the demon realm especially with the ascension of more demonic cultivators in the demon realm due to presence of stable foundation inform of contracted powerful demons.This increased the number of demonic cultivators as they finally didn't have to ascend to the heavenly realms where rumors said they were heavily oppressed.
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Unbeknownst to those of the lower realm, the introduction of the Jing system had set off waves in the upper realms as it facilitated trade between species that hardly trusted each other and if that was all it wouldn't have mattered that much yet this led to a mass exodus of demonic cultivators to the demon realm which reduced the fighting power of the heavenly realms heavily.
As more humans entered the demon realm and formed factions, more rules were set by the demon emperor favoring no one in particular allowing for development. And with the presence of humans who are highly capable in civil works, the work became faster yet it even became faster than that when they heard that all one has to do to become a citizen is sign a deal with the demon realm that one shall not cause harm to the demon realm and as for infighting and killing, that was allowed as long as not done on behalf of other planes.
With a place where only ones fist only truly mattered, the powerful demonic cultivators started setting up sects in the demon realm giving foundation to humans and forming friendships with demons whose standing had drastically increased.