When I asked Marco and the other human adventurers about this question, they said they didn’t know. However, Debra, who has the most knowledge among the Four Heavenly Kings of the Demon King’s Army, surely knows the answer.

"Ah, I haven’t explained that yet, have I? The war 300 years ago was triggered by the betrayal of the humans."

"A betrayal by the humans..."

"That said, at that time, I was not yet one of the Four Heavenly Kings of the Demon King’s Army but merely an undead. So this story is not something I personally witnessed but rather one I heard from those who were there."

"................"

I had my suspicions, but it seems this Debra fellow has been alive for more than 300 years. The fantasy world is amazing...

"Back then, there was a country called Walthea located on the border between human and demon territories. Despite its small size, it was a peaceful nation where humans and demons coexisted."

I remember hearing that before the war, humans and demons used to live together.

"But one day, without any warning, a human army suddenly invaded the country. The demons living there were slaughtered. Of course, the demons resisted, but it was a surprise attack, and even the humans living in the country sided with the invading army, leaving the demons with no chance."

"................"

"The demons at the time were naturally enraged by this betrayal and began attacking human nations and towns. In response, the humans fought back, and this marked the beginning of the war that has lasted for 300 years."

A betrayal by the humans, huh...

Even if the war started because of human betrayal, it seems like it's too late to use that as a reason to stop this war that has dragged on for so long. If the cause was something simpler, like the demons' treasure being stolen, there might have been a way to resolve it.

"...I understand the situation to some extent. I’m willing to help if a few conditions are met."

"Really, Demon Lord!?"

"What are those conditions?"

"Well..."

I’ve come up with a few conditions for helping the demons.

First, they need to gather the Magisteel Crystals I need to return to my original world, but only as much as is reasonably possible. I’m not in a hurry to return, and I have things to take care of with Lutra and the others, but I want to at least prepare for my eventual return.

Second, they must minimize harm to humans as much as possible. Even though this is another world, the people we are dealing with are the same as me—humans. I don’t want any direct conflict if it can be avoided. Of course, unless my life is truly in danger, I have no intention of killing anyone.

Third, we must aim for a ceasefire in this war. It’s been going on for so long that even if I show the power of a Demon King, the humans won’t simply surrender or stop the war. For now, the goal should be to bring the war to a halt.

Surprisingly, both Libera and Debra agreed to these conditions. I thought they might demand some concessions on the second and third conditions, but they seem willing to accept them.

I’m not sure about their true feelings, but it seems the demons are so cornered that they’re willing to agree to anything at this point.

"But, Demon Lord, there is one problem."

"What is it, Libera?"

"While we two have no issue with these terms, the other two of the Four Heavenly Kings, Jilbe and Lugaro, will likely oppose them..."

"I believe the same. Especially Jilbe, who lost his entire clan to the humans, holds an even greater hatred for them than most demons. He’ll likely want to continue fighting until the humans are exterminated."

Jilbe... if I recall correctly, he was the large wolfman with the beautiful silver fur who attacked me first.

Upon hearing more details, it seems Jilbe’s clan, known as the Silver Wolves, had fur that was prized by human nobles and aristocrats. When the war between humans and demons began, the humans immediately targeted the Silver Wolves.

Now, Jilbe is the last of his kind. Hearing that, I can’t really argue against the idea that humans are cruel...

"What about Lugaro?"

He’s the one who shot fire magic at me. Like Alex, he had blue skin, but he also had two horns sprouting from his head. Outwardly, he looked the most like what I imagined a demon to be.

"Lugaro didn’t lose his entire clan, but his parents were killed by humans. He also seeks revenge on them, so I doubt he’ll agree to your conditions, Demon Lord."

"I see..."

So, just like Alex, he harbors a deep grudge against humans... I suppose expecting them to follow my soft stance of not killing humans is unrealistic.

More than that, it will likely be difficult to even get them to recognize me, a human, as the Demon King.

"...What about you two? Did you lose family or close ones to the humans as well?"

"In my case, I didn’t have any family to begin with. While my kin have been killed, it’s not something unique to me; both sides suffer losses."

"My father was killed by humans, but it’s a war, so I’ve accepted it as part of the conflict. What’s more important now is to prevent any further suffering of the demons!"

It seems that even among the demons, there are various ways of thinking.