"I shall show you. This is the final... Moon Breathing."
In the end, I have become a Demon.
A Demon Slayer turning into a Demon... what a godforsaken irony.
It seems the prophecy came true after all. What is this, some kind of Norse tragedy?
Hmm... I feel a certain hunger, but I don't feel the slightest urge to devour Ruka Amano or the other Hashira.
Is it because I consumed Muzan's heart...? Or is it a latent perk revealed only now because I am a reincarnator...?
Or perhaps, I am simply a unique case among monsters.
More importantly, the sensation of being a Demon is quite pleasant.
I think I finally understand why Muzan and his ilk were so insufferably arrogant.
When I first mastered Breathing, I felt I could do more than ever before. Now, it feels as though I can do anything.
Even if a limb is severed—a fatal wound for a man—it would regenerate in an instant.
No matter the distance, there is nowhere I cannot reach.
No matter how sturdy the defense, it would surely crumble before a single one of my strikes.
Truly, I alone am the honored one beneath the heavens.
Well, even with all this, I still cannot imagine defeating Yoriichi.
Good grief, what kind of monster are you, really?
Enough reflecting.
I will now pour every ounce of this power into the singular goal of slaying Muzan.
This is likely the end.
"The 'Final Moon Breathing'... is for me to become a 'Demon' myself."
My blood transformed into a dark haze, swirling around me.
"By using this technique, I lose all my humanity. That is the meaning of 'Final'."
"What... What are you?! How can you escape my dominion, and more importantly, how can you maintain your sanity and radiate such power the moment you turn?!"
Muzan screamed, his voice laced with venomous spite.
Emotions flickered in his eyes.
Doubt, disbelief... and.
Fear.
It was the primal terror one feels when facing something unknown that defies all reason.
"Are you afraid? To see the impossible unfolding right before your eyes?"
I'm the one who should be afraid. Even pouring out my entire soul, I have no certainty that you will truly die.
But I must do it.
I raise my empty right hand.
A bare hand, holding neither a Nichirin Blade nor any other weapon.
I am not trying to use some 'Incorporeal Sword' or 'Mind Blade' from those martial arts novels.
I don't know if this is my Blood Demon Art, but something has come to mind.
I am simply following my instincts.
Just as I did when I created Moon Breathing.
Just as I did when I forged new Forms.
Just as I did when I manifested the Mark.
Just as I did when I reached the Transparent World.
Just as I did when I manifested the Crimson Blade.
There has never been a time when I wasn't improvising; I simply cast my will out into the void and these powers were the answer.
So, this will be no different.
I take reference from the Blood Demon Art of my doppelgänger I saw at the Sanzu River.
Did he not maximize lethality by attaching countless miniature blades to his sword aura?
I create miniature blades just like him.
The difference is that I make them far, far smaller and exponentially more numerous.
Individually invisible, but together, they form a single line.
An infinite number of blades connecting to form a single black stroke.
And I visualize the strongest existence I know—Yoriichi.
Yes. If it is this, it should be enough to return that wretch to nothingness.
A two-dimensional being cannot interfere with a three-dimensional one.
But what if one transcends the boundaries entirely?
That is the madness I am about to attempt.
I already ate Muzan's heart; what's one more act of insanity?
Well, since I've improvised this without a single thought, I haven't considered if I can ever use it again...
Focus.
Connect the points to make a line, and swing that line to create a plane, returning space itself to nothingness.
Hooooooooh.
Moon Breathing.
Final Form: 「Mugetsu」
I gripped the black line and swung it down upon Muzan.
In contrast to the Full Moon that lights the dark night more brightly than any other, this was the 'New Moon'—the absolute void. As its name implies, every color in the world was inverted into monochrome black and white.
A single black line traced through the air, too swift for even the King of Demons to react.
A moment of silence followed, for the strike had severed even sound itself.
SHUUUUUU—BOOOOOOOOOM—!!!!!
In that instant, the monochrome world bled back into color, and with Muzan at the center, the entire mountain behind him split in half.
I stared at the sheer scale of the destruction with a bitter expression, while the surrounding Hashira were frozen in terror.
It's a mercy no civilians were nearby; I didn't expect the power to be this absurd.
To think I didn't just cut Muzan, but bisected the mountain behind him as well.
I... I actually split a mountain...!
In that moment.
Suddenly, all strength left my body.
It seemed that act was an attack that pushed 'overextending' to its absolute limit.
I had poured every drop of blood I possessed into that single technique.
Even after consuming the heart of the Demon King, this technique seemed beyond my capacity.
I might never be able to use this again...
But at least Muzan is de—?
What?
Muzan began to writhe, his flesh regenerating once more.
He can still regenerate after taking that head-on? Just what is this guy made of?
Hey, you bastard, dragging it out this much is just bad writing. Are you some kind of immortal Valkyrie from hell?
Then, once more, I'll use Mugetsu—
My body suddenly gave way, collapsing as if refusing to obey another command.
My knees hit the ground, and it was all I could do to keep from faceplanting by bracing myself with my hands.
I can't get up.
"Lord Tsugikuni...!"
I... have no... strength left.
Neither Amano, nor Rengoku, nor any of the other Hashira are in any condition to move...!
Damn it, is this the end?
Muzan stumbled, but he was slowly forcing himself upright as his regeneration neared completion.
Decapitation doesn't work... Mugetsu doesn't work... Is it over?
At that moment.
I felt it.
Someone was sprinting toward this location.
I don't know if it's intuition or the resonance between those who bear the Mark, but someone is coming.
The 'Deus Ex Machina' who will shatter this wretched situation...!
***
It was at that fleeting second.
I couldn't sense a single thing from him.
No Battle Spirit, no bloodlust, no pressure, no hatred.
All the energies that had been surging infinitely until moments ago vanished in a flash, as if they had never existed in the first place.
Even though my very flesh screamed a warning that the black line in that man's hand was lethal...
I felt no presence from him at all, which is why I had no choice but to let that black line carve right through me.
A black line that split the world.
An earth-shattering power that not only tore through my immortal body but split the mountain behind me.
However, while his attack could return existence to nothingness, it could not kill me.
In this paradoxical clash between an immortality that can only be ended by the sun and a power that returns all to nothing, the victory belongs to me.
It took much longer to regenerate than from any attack I'd received in the last five hundred years, but—
None of them have any strength left to move.
I survived.
It seems 'God' truly does not exist in this world.
I mocked the non-existent gods and looked down at the man on his knees.
I still do not understand how he escaped my control, or how he could wield such power while remaining sane as a fledgling Demon, but it no longer matters.
He failed to kill me.
"Tsugikuni Michikatsu, this is your defeat."
It is a shame I cannot possess you, but that power you used—
If I consume it, I will have gained the ultimate spear.
Even if the buzzing flies of the Demon Slayer Corps' Hashira appear in droves, no one in this world can be my match unless they possess the power of the sun.
I gathered blood in my right arm; it swelled grotesquely, sprouting massive jaws and pupils, writhing like a living beast.
"This is the end, Tsugikuni Michikatsu...!"
Just as I was about to devour his flesh—
"Pfft!"
Hm?
Suddenly, Tsugikuni Michikatsu laughed.
"Pwahahaha—!!"
What? What is so funny?
What on earth are you laughing at?!
Do you have some other hidden trump card?
Absurd. Neither you nor any of these Hashira can move a muscle.
In this despair, what could you possibly do to justify that laughter?!
"What... is so funny?"
"Muzan, you are a fool."
Kuooooooooo.
"You probably haven't even realized why I didn't include myself in the five special threats."
He mocked me, holding up his middle finger.
"What nonsense—"
In that moment.
"You're too late, you son of a bitch."
Someone was sprinting from behind Tsugikuni Michikatsu.
Red hair, a crimson Mark engraved on his forehead, a blade burning bright red, and earrings depicting the sun fluttering by his ears.
'Tsugikuni Michikatsu?'
That man was a spitting image of Tsugikuni Michikatsu.
But that man is kneeling before me... then, who is this?!
His face was contorted with a rage beyond measure, but in stark contrast, I felt no Battle Spirit, no bloodlust, no pressure, and no hatred.
It was a sensation similar to when I faced the Michikatsu who held the black line.
But unlike then, my body sounded no alarms.
A frail man, a moth flying into the flame.
My body seemed to say this man wasn't even worth my attention.
Who is this man—
Wh—
Sun Breathing.
I wasn't caught off guard.
I had finished regenerating from the previous attack and was already in a combat-ready state.
And with this madman right in front of me, there was no way I'd be careless.
I simply blinked.
After perceiving his presence, I simply blinked my eyes.
Just once.
That was all it took.
「Thirteenth Form」
SLASH—!!! SLASH—!!! SLASH—!!!
Cause, process, and effect.
All of them happened simultaneously.
The tentacles were shredded in an instant, and all five brains and seven hearts were carved through.
My head fell from my shoulders.