Ten thousand years ago, the humans and Demon coexisted peacefully with each other.
The demons had started appearing randomly across the world. At first, humans acted hostile towards them and tried killing them.
They soon found this task impossible to pull off. They thought it was a full scale invasion and were terrified and tried to surrender.
This was when the oldest and first demon, the demon king Lucifer, came up to the leaders of the world and cleared up the confusion.
He explained how the demon world was over crowding and they needed a place to stay.
The humans at first hesitated due to how the demons looked. They were monstrous and looked like creatures straight from a nightmare you prayed would never come true.
He explained about the different level classification of the demon world.
The demons are classified into 7 tiers. The 7th heir being the absolute strongest where only two demons resided at the time.
Demon king Lucifer and the Prince of destruction Azazal, the only 7th tier demons.
The humans finally accepted Lucifer's plea for help when the demons showed they can assume a human form.
For many years the humans lived in harmony with the demons. But as time went by humans were worried by the insane population growth of the demons.
Humans turned to science and God for an answer . After years of continued research and fruitless prayers , their prayers were finally heard.
They had successfully made 'the divine blood. An artifact capable of releasing one's true potential and allowing them to exceed their physical limits.
The humans who manned to be compatible with the divine blood were known as exorcists.
Humans with insane strength and divine super powers that allowed them to go toe to toe with demons of similar level.
The exorcists too had their own classification system, the star system. This was measure via a device know as the lord knows all.
They were classified in star ranks from one star to seven star exorcist. With 7 being the absolute pinnacle of the exorcist ranking.
Once the humans fully established the exorcists in secret, they then provoked a few demons into destroying a village. Which the demons did.
The humans used this as an excuse into waging war on the demons. At first , Lucifer was not worried as no human weapons could harm demons.
When the war started the demons were taken by storm by the exorcists who appeared out of no where.
When Lucifer learned of this , he was enraged. He personally came to the human world and fought the 7 star exorcists at the time.
It was an intense battle and all the 7 star exorcists sacrificed themselves to seal Lucifer.
After this , the war still continued on for centuries. The exorcist began becoming stronger and more better developed over time.
To this day Lucifer is pissed off at the demons the humans wrongly killed and some even experimented upon.
He warned them that in a couple centuries time a new 7th tier demon will appear and change the course of history, forever.
And so the peace was broken and the war has raged on for thousands of years until know.
When a mysterious demon girl appeared in the world and was adopted by a Noble family, the Valentine family.