As far back as the world can remember, humans and demons have always been at war with one another.
No matter which side prevails, the war has always ended in a hopeless stalemate where both sides are forced to take a step back for what is ultimately referred to as the "Perpetual Truce".
"A cruel endless cycle of fate fueled by an existential rivalry that never ceased," stated Great Scholar Soleil.
As one would have it, every war had always ended with both the Demon King and the Hero dead.
As long as a Demon King is alive and kicking, new heroes will be born in place of dead ones to judge its sins. In turn, a Demon King can never truly "die", and so does the Demon race as a whole.
When a Demon King is subsequently "slain", a new Demon will emerge after a certain amount of time to inherit the throne as well as the previous's leftover army. Being the sole being able to procure new demon life, it's rather similar to a queen ant. The only difference is that a Demon King's strength grows accordingly with the time spent alive, as well as their army.
However, a few hundred years ago, with the eventual sacrifice of Great Scholar Soleil and Hero Omid, humanity had finally managed to seal the "Demon King", ending the Great 7th Cataclysm abruptly.
By doing this, humanity effectively stunted the growth of the Demon race as well as weakening them by a great degree indefinitely.
This would be the first turn of events in an unimaginably long time to shake the world's established foundation.
While humanity has yet to come up with a sufficient way to kill the demon king even til now, they were able to wipe out 99% of the Demon race during the following centuries, rendering them near extinction.
When all hope was lost for the Demon race, a saving grace descended....in the form of a Unique Demon named The Prophet.
From the other side of the space rift, it came to pass a prophecy that the demon king's imminent return was to happen in 500 years' time, as well as an ambitious plan to bring their race back from dust.
***
Fier.
That was the name he was given as a nameless demon child.
He still remembered it vividly...the day he was granted another chance at life.
On that freezing night, lying on the hard cold stone floor as he bled out, he lamented his fate.
A measly hundred years after the Demon King was sealed, the human was still fully committed to chasing every remnant of the demons down. Everywhere he went, somebody was already lying in waiting to go after him. Be it ancient ruins, deserts, forests,…there was no place for him to go.
Nevermind the active oppositions and the neutrals, even races that were once close allies had turned their back, and some were even willing to join in the "fun", enjoying the pathetic sight that was once the most dominant warmonger race.
At that point, even the 10 Dark Lords were struggling to survive, lest someone who barely gets by in his own realm like him. Fortunately enough, with his frail small body, everyone he had come upon always underestimated him, giving him a chance to use [Suggestion] and slip out. Albeit, [Suggestion] is only a degraded form of [Hypnotism], which meant luck was an important factor…
And his luck wouldn't last so long.
After arriving in Surgeli - The Kingdom of Frost located in the far northeast, he'd, most unfortunately, meet one of The Lumbers, those that [Suggestion] didn't even make flinch.
One chop was all it needed to send him into such a state, and even though he somehow got away once again, death was the only thing that awaited him this time.
He knew his time would soon come to an end, but he didn't expect, or rather, wanted it to be in such a lonely, dark place. In the end, only a taste of bitter deceit lingered on his tongue, not the sweet glory he had once dreamt of once he matured.
He lacked strength, too much of it. Even the [Suggestion] he had so much pride in for saving his ass so many times had finally failed him, so what could he even be proud of?
It seemed as if he was destined to meet a dead end from the start.
The more he thought about it, the more he could only clench his teeth helplessly, his heart in tatters.
He wanted to do more...no, he HAD to do more. There was no way he'd let things end this easily when he had gotten so far even when all odds were against his kind.
A desire to live was rekindled then, but it only despaired him even more. There was nothing he could do to save himself.
As footsteps drew closer, he closed his eyes and bit his lips, finding himself unable to truly accept his fate.
However, things weren't as they seem.
"Oho? What an interesting fella I found."
It was undoubtedly a unique scent unbelonging to demons, but the strange figure wasn't adamant about finishing him.
Rather, he seemed...amused.
***
"This revolting feeling...That must be it!"
In the world, there exist only two types of energy that counteract the very essence and existence of a demon, namely Holy Energy and Divinity. Nevertheless, what he sensed was a mix of 2, just like what that PERSON told him.
This meant whoever it was ahead was definitely born an absolute counter to them all. To accurately describe that human, it would be what a Demon King is to humanity.
"Monsieur was right. I have to deal with it now. If we left it to grow..."
Demonkind would truly face extinction.
***
After bringing him home and nursing him back to health, the mysterious figure revealed himself to be the Prophet. They expressed a desire to save the demonkind and wanted him to join in the plan, seeing his potential and all.
The little demon, though expressed interest to partake in such a plan as there was nowhere he could go anymore, was also filled with doubt. Thus, he promptly inquired about this "potential" the Prophet mentioned.
"Have you ever heard about the 5th Demon King?"
He shook his head.
"I see. To bring into perspective, she was probably the most dangerous out of the 7 humanity has faced until now, even though she was neither the strongest nor the wisest. Why is that?"
Confused, the little demon tilted his head.
"You know how humans can turn into demons under the influence of demonic energy, right? However, that only applies to weak-minded humans most of the time."
He nodded vehemently, elated to hear a piece of information he actually knew something about.
"What makes the 5th truly dangerous is her ability to do this to ANY human without exception, as long as the conditions are fulfilled of course. With it, she had managed to turn many aspiring young warriors as well as powerful veterans from humanity."
Though the records weren't clear, it is said that even the most strong-willed can falter to such a fearsome ability.
"And you see...You can master it as well. Or rather...I need you to master it."