A Demon King Through The Worlds

Why do ships gradually disappear from below as they sail towards the horizon? Answer: the curvature of the globe gradually makes it impossible to see ships.

Why do the stars twinkle? Answer: Because the stars (which are not the sun) are very far away, their light ends up being deflected several times by atmospheric gases, causing them to flicker.

Both are apparently silly questions, but the answer to one of them changed the way people saw things. The fact that "the Earth is spherical" changed science and religion, it changed how people would make physical calculations, it changed how maps are made.

And the other answer is just an astronomical curiosity.

Even a seemingly silly and unimportant question can change a lot of things. A question is often the precursor to an answer.

They are necessary for progress to be made.

They make improvements happen.

... Wait, why am I making such a big deal out of the act of asking?

Leaving that aside, a question popped into Lucian's mind as he walked through the streets of Tokyo.

"What's the difference between ordinary demons, Akaza and Muzan being beheaded?"

First it is necessary to point out why beheading was the only way to kill them. In the past, sunlight was able to kill the cells of demons, causing them to disintegrate at a cellular level.

Nichirin blades contained sunlight/energy, so they were used to kill demons.

But why are all injuries other than to the head not fatal? Because the brain is the most important organ in the body and the one that controls all the others?

But if that were the case, injuries to the heart could also be fatal. After all, if the blood isn't pumping and the brain runs out of oxygen for too long, it will die.

But even if a demon had a stake in his heart for hours, he would still be completely fine, unlike his vampire cousins.

So why?

"The brain acts as the connection point between the body and the soul." Although he still couldn't touch the field of souls, Lucian knew very well that they exist.

He felt it vaguely... like air, you can't see it, you can't "touch" it, but every now and then you can feel it.

More specifically, when it "moves", in other words, the moment when he felt it most clearly was when he "died" and his soul wandered freely through the worlds.

While the soul remains in the brain, it is not really in it.

In humans, when the brain dies the soul detaches from the body, so there are a few things that can happen: it dissipates, goes to an "afterlife" plane where the souls of the dead reside or through obsession or resentment it forms a spiritual body and becomes a ghost.

In demons, ordinary physical attacks are not capable of causing real damage, but when they used the nichirin, the blows really hurt the demons, so blows to the head break the body-soul connection, and the reason for decapitation being the preferred method for this... it's easier to cut a neck than a skull.

The demon of time, the first demon Tanjiro encountered in Kimetsu no Yaiba, could be killed with a stone because its body had fallen off a cliff and its regenerative capabilities had already been exceeded, leaving only its head, the only thing it had left. And with a high degree of destruction to his head, he would eventually die.

On the other hand, Daki once had his head almost completely destroyed by a kick from Nezuko and was able to heal peacefully, as he didn't receive any "real" damage because it was a simple kick. So the soul remained connected and its regenerative capacity remained functional.

In short, demons can be killed by physical attacks, but the attack in question would need to be at the level of Might Guy or Saitama to be able to do so.

In a much more complicated situation, when Akaza was decapitated by Tanjiro using the Hinokami Kagura, he didn't just die, he died solely and exclusively thanks to his powerful spirit and strong willpower, his soul stubbornly clinging to his body. Although he gave up fighting after recovering some memories of when he was human and this caused his death.

But the point is: a demon can sublimate its regenerative capacity through a sufficiently powerful will – which, in a way, demonstrates the strength of the soul.

And Muzan... he had five brains, which is five connection points, so the thirteenth form of the sun's breath is needed to kill him. Seven hearts pumping blood to enhance physical capabilities, five brains helping to process information and serving as "backup points".

Although Lucian is very fond of criticizing Muzan, he still had to admit that this idea was simply great.

Multiply the vital points and the difficulty of killing you increases exponentially.

This is what differentiates the "demon king's body" from that of the other demons; this is what ensures that the demon king is more powerful than the other demons on an "equivalent" level.

"That must be what he's done for a thousand years." He nodded as he came to this almost totally irrelevant conclusion, at least for the moment...

But an idea was slowly taking shape in his mind...

Just then, however, something snapped him out of his frenzied reveries – someone bumped into him.

A slender young man with white hair and sutures all over his body. A few staples in his hair formed the Roman numeral equivalent to thirteen, "XIII". Another striking feature was his red eyes and the deep circles under them.

'With such a feminine face, I'd certainly think he was a woman... not that he's very far from being one.' Lucian looked appraisingly at the young man in front of him.

With such obvious features, especially the sutures, it didn't take him half a second to recognize that this young man was Suzuya Juuzou.

"Are you disappointed not to find a wallet?" Lucian raised an eyebrow, looking at Suzuya somewhat sarcastically.

He had felt a hand reach into his pocket and realized that he had practically occupied Kaneki's position in the scene where he is robbed. It's a good thing Lucian doesn't have a wallet, otherwise it would have "almost" been stolen.

'He almost stole the wallet I don't have.'

Of course, Suzuya walking down these streets also meant that the Aogiri Tree wasn't far from attacking and capturing Kaneki.

"A little." Suzuya smiled broadly when he heard that, not at all bothered by being found out.

"You know, young people like you shouldn't go around doing things like that." Lucian slung his arm around the shoulders of this young man who was wandering aimlessly through life.

As an upright and altruistic person, he felt obliged to help this poor young man who had suffered so much in life.

But again, looking at that rather feminine face, he wondered if Suzuya really was a man.

'Well... the face and other rather feminine features, such as the slender physique, can be explained by a severe testosterone deficiency, stemming from the castration that happened to him.'

"Oh, what am I supposed to be doing?" Suzuya tilted his head slightly, curiosity evident on her face.

"..." For the first time in a long time, Lucian didn't know what to say.

'What was I doing at that age? ... it doesn't make that much difference, but at least I wasn't knocking over desks. Then he said: "I don't know, going out with someone maybe? Or playing video games, having fun and all that young stuff."

"That seems to make sense." Suzuya nodded, pickpocketing isn't exactly a way to have fun, 'Maybe I should butcher someone?'

Maybe the definition of fun is different for him.

"In case you don't mind, I have other things to do now." Putting that aside for the moment, Lucian said goodbye, intending to make his way to Anteiku.

'I have to say, though, he does look like a little doll... of terror, but he's still a little doll.'

(I wonder if Suzuya should be added to the harem. Just kidding... or is it?)