Kkulf Kkulf, the 1st Demon King, was a 4.7 km monster. He would drain the blood from creatures over a several mile radius using a vast array of tentacles, and had rapid regeneration abilities and could recover from most injuries with relative ease. He had 8 eyes in total, 3 on either side of the main body and two at the end of an appendage that took the form of a woman.
The main body was octopus-like in appearance, his brain was encased in a semi-transparent hardened shell on his head, the most defended part of its body. Kkulf Kkulf lived for 5000 years, until he started a war with the Dragons. Kkulf Kkulf was killed, but the final blow was struck by a dragon named Avel, brother of the Dragon King. He drank the blood of Kkulf Kkulf and, in the process, became the 2nd Demon King.
Avel turned on his kin, and after only 56 years, was sealed in a dark dimension. For the next 665 years, there was no Demon King. Then Avel, finally giving up on escape, killed himself. Thus, the beginning of the system of power transfer, as the power bled from the dark dimension, and into the first being it encountered. Thus, the 3rd Demon King, Ssulal; the first human Demon King.
Due to the way her powers were gained, her body was actually quite frail, though she was incredibly intelligent. It was her work in experimenting with her powers and other magics, that she was able to discover the nature of her powers, and then stabilize it, making the transfer more effective, and less dangerous for the next host. One of her experiments eventually killed her, however, after only 500 years.
The power transferred to one of her children, Nighcisa. Nighcisa was the start of the animosity between humans and demons. He was a heinous, brutal character that had no feeling but malice for mankind. Nighcisa was much more attuned with his bloodlust than any other Demon King, frequently appearing in random villages across the continent to consume the blood of the innocent. The most vampiric Demon King, Nighcisa was a savage and uncaring monster that saw humans as toys for him to play with, he cared not for them or his own kind. It was for that reason that Nighcisa was the only Demon King that Xavier ever pledged his absolute loyalty.
Nighcisa, 901 years into his reign, declares war on humanity. 3 years later, 50% of humanity has been wiped out. However, he is gravely injured by an unknown hero with a holy sword in the process. Nighcisa begins looking for a successor. He encounters a girl named Gele. Fair skinned, with soft hair and pretty blue eyes, Gele was a girl who could be called faultless, intelligent, incorruptible and beautiful. Unfortunately, these virtues brought spite and jealousy from others. In the last years of Nighcisa's reign, Gele was kidnapped, raped and torured by people that hated her pure virtues. Her limbs were severed and she was left to die. Nighcisa happens to come upon her, and for the first time, feels compassion and pity, and chooses her as his successor, giving her his blood.
Gele, the 5th Demon King, and the most savagely brutal Demon King of all time. Because her last memories before becoming a Demon King were that of the cruel treatment she suffered at the hands of her attackers, her world-view was warped into an intense hatred for humans. Before becoming the Demon King she had already lost her mind. While she could still think intelligently, she was no longer rational and vented all of her worldly hatred upon mankind.
Cunning and brutal, Gele subjugated mankind to a life of slavery with several well-laid plans. 321 years into Gele's reign, she declares open season on humanity, and orders all her subjects to hunt down and massacre humans at their leisure. After destroying all the unified kingdoms of mankind, she enslaved humanity, forcing them to work and breed until they died of exhaustion.
1004 years into her reign, her most trusted follower, and her lover, Gi, betrays her. He forcibly takes the Demon King power from her, and seals her away in a dark dimension, much as Avel was in the past. He then destroys all traces of information on how to steal the power as he had done.
The 6th Demon King, Gi, had split personalities prior to becoming Demon King, and was originally human. Was turned into a demon by Gele. When he became DK, his appearance was altered to match his split personalities; His body was literally split down the middle after he became Demon King, with one half representing his kinder human side, and the other representing his callous and darker side.
Wise and charismatic, Gi did not seek conflict with the Human race. He adopted a policy of noninterference with the world of humans, commanding all Demon Lords to leave humanity alone, this caused a lot of controversy amongst the Demon Lords. He often had times when he would temporarily lapse into his second personality, he was said to be quite violent and cruel during these times.
Because of his noninterference policy, human kingdoms were able to be founded. It was 24 years into his reign that he freed humanity from the slavery Gele had them under. 420 years into his reign, another Demon/Human war breaks out, due to people who disagree with Gi's policies. 500 years into his reign, Xavier returns in Japan, end up being split into 8 parts and sealed.
850 years in, Gi goes on a bit of a 'spree', trying to create a suitable heir. This results, eventually, in his daughter, Hornet. Things remain pretty tame for the next 2065 years. Then, for unknown reasons, 643 years ago, he kidnaps Miki from the future, passes his power to her, and allows himself to be killed. He tells his dying will to Hornet, in which he wished for her to "protect Miki, make her the next Demon King, and establish peaceful coexistence with humans."
This causes two factions to raise up in the Demon Realm; the Kayblis and Hornet factions. Those who follow, or at least agree with, Hornet, and want Miki to take up the mantle of Demon King. And those who follow Kayblis, who has been around since the days of Kkulf Kkulf and was his first servant, who wants to kill Miki and consume her to become the next Demon King.
The Kayblis and Hornet factions did not go to war, but fought behind the scenes while the various other fighting was going on.
