The battle continued within the Infinity Castle.
To the great surprise of all, Doma ultimately did not escape his fate.
Due to the counter-effectiveness of the Flame Hashira, Kyojuro's Flame Breathing, and the desperate struggle of Sanemi and Muichiro, who had multiple Upper Rank heads to their name, Doma, having expended too much demon energy early on, was no longer a match. After gravely wounding the three of them, he was swiftly decapitated by Kyojuro.
"Ah, what a pity. I still wanted to save more people." His will to survive was never particularly strong, and he failed to break the demon's boundaries, slowly fading away within the Infinity Castle to his ultimate destination: Hell.
Kyojuro and the other two, having sustained varying degrees of injury, took a brief rest before dragging their weary bodies in search of Muzan.
Muzan was currently in a frenzy of rage.
"Worthless! Worthless! All of them are worthless! Gyokko and Hantengu dying was bad enough, but now even Doma is gone, and Akaza and Kokushibo together are still taking so long to defeat that swordsman!"
Muzan tugged at his necktie, his expression icy as he said, "Fine. I must personally intervene and retrieve the key to evolution that is rightfully mine!"
After observing Aomori for some time, Muzan believed he could crush him effortlessly. He was also certain that the man who previously threatened him was not in the Infinity Castle, so intervening personally was acceptable.
"Nakime! Transfer that swordsman to me. Have Akaza and Kokushibo deal with the other swordsmen."
It didn't matter if they failed to defeat them; he only needed assurance that no one would interrupt him before he finished absorbing the swordsman.
Nakime nodded, and the sound of her Biwa slowly began to play.
...
"Destructive Death: Crushing Style – Ten Thousand Leaves Flashing Willow!"
"Moon Breathing, Sixth Form: Perpetual Night, Lonely Moon - Incessant!"
"Thunder Breathing, Sixth Form: Rumble and Flash!"
Fists, crescent blades, and lightning intertwined, causing round after round of booming noise.
Aomori, Akaza, and Kokushibo fought fiercely, and three rooms had already been destroyed by the residual force of their battle.
Using only Thunder Breathing, Aomori relied on his incredible physique and marginally superior speed. Coupled with the poor coordination between the two Upper Rank Demons, he gradually gained the upper hand in the fight.
Akaza, who dodged Aomori's sword strike only to be cut by Moon Breathing, was once again kicked out of the main fight by the two. He couldn't help but roar, "Kokushibo! Get out of my way! He is my prey!"
The lust for battle caused Akaza to forget his emotional intelligence.
"It is you who should step aside. If not for me, you would already be dead," Kokushibo said coolly. He also craved combat with powerful opponents, as it honed his swordsmanship.
Aside from Muzan and Yoriichi, who completely overwhelmed him, he had yet to meet someone like Aomori who fought him to a standstill. He believed that achieving victory would allow his swordsmanship to advance further.
"Damn it!"
Just as Akaza was about to burst out in anger, the scenery before him changed. He could no longer see Aomori or Kokushibo.
"Nakime?" Akaza, having slightly calmed down, learned of Muzan's new order in his mind. Reluctant as he was, he could only accept it.
Then, Akaza encountered three swordsmen, two men and one woman. Taking one look at the female swordsman, his brow furrowed.
Kokushibo, having the same experience, ran into Gyomei and Giyu.
And Aomori, after more than 20 days, finally stood before Muzan again.
The plan, named "Luring the Snake out of its Hole" after the initial "Beating the Grass to Startle the Snake," had achieved perfect success.
...
In the deepest room of the Infinity Castle, Aomori and Muzan faced each other.
Looking at Aomori, clad in a yellow-striped haori over a black Demon Slayer uniform, Muzan's eyes burned with eagerness. He took a deep breath, and the slightly sweet scent of blood entered his body, causing his demon blood to boil.
Muzan couldn't help but spread his arms, tilting his head back, and exclaimed excitedly, "Yes, it's you! It is you! Come, merge with me! Become the perfect being immune to the sun, become the eternal God of this world!"
Aomori pointed his sword at Muzan and said calmly, "I refuse."
"Why refuse? Is becoming an invincible, eternal existence not good?"
"Heh, the last invincible existence ascended to heaven. Do you want to ascend too?"
Muzan, not understanding what Aomori meant, sneered, "Refusing won't help. You are mine."
As soon as he finished speaking, Muzan's clothes burst open, his black hair quickly turned white, his limbs and lower body were wrapped in blood and fur, massive mouths lined with sharp teeth erupted across his body, and long whip-like tentacles extended from his back and legs.
Muzan had transformed directly into his final form!
The dozen or so tentacles whipped through the air like long serpents, lunging at Aomori with brutal force that seemed to rip through space.
Aomori held a sword in each hand, continuously swinging his Nichirin Blades to parry all the incoming tentacles.
Such immense strength. Aomori's hands were left numb from the impact. He was forced to fight defensively while retreating. However, even in terms of speed, Muzan was unparalleled.
As expected of the Demon King. Even without any flashy Blood Demon Arts, this sheer strength and speed alone were enough to utterly defeat most people—though the cheat, Yoriichi Tsugikuni, was not among them.
Facing Muzan head-on now, Aomori realized how wise his initial decision to strike him preemptively had been. If he hadn't gravely wounded Muzan when he was unprepared, Aomori's chances of decapitating him would have been even slimmer.
But in the course of the battle, Aomori noticed a flaw in Muzan.
That is, compared to demons like Kokushibo, Muzan's battle awareness was noticeably poor.
This is not to say that Muzan made combat errors. On the contrary, with his three brains, he was like a machine, testing Aomori's blind spots and weaknesses. Every move was calculated to perfection, down to the last millimeter.
But because of this, Muzan lacked flexibility. To him, in a situation where sheer power was enough to crush his opponent, why would he need to change his attack pattern?
Muzan utterly hated change; he demanded that everything be under his control. From this, one could understand his immense fury over the failures of Doma and the other demons.
Therefore, to avoid being slowly worn down by Muzan, Aomori decided to introduce an unexpected variable.
Thunder Breathing, Fourth Form: Distant Thunder - God Speed!
With the added boost of lightning energy to his feet, Aomori burst forward at a speed surpassing Muzan's, breaking through the blockade of the tentacles. As he closed in on Muzan, Aomori gripped his left sword with his teeth, freeing his left hand. A cylindrical object appeared in his empty palm, which he hurled at Muzan before accelerating even faster to zip past the Demon King.
"Take my ultimate secret weapon!"
"Secret weapon? What kind of secret weapon could possibly harm me?" Despite saying this, Muzan valued Aomori highly, as Aomori was only the third human with this level of power he had encountered in his long life. Muzan attributed Aomori's strength entirely to the boost provided by his Rare Blood.
Muzan, now even more eager to possess Aomori, decided to be cautious. He protected himself with a gigantic hand that grew to human height while swatting the "secret weapon" away.
However, when the "secret weapon" made contact with the gigantic hand, the fragile object burst open. Simultaneously, an indescribably revolting stench was inhaled into the lungs of Muzan, whose six senses were operating at maximum capacity.
"Gah! Ugh..." Muzan instantly vomited.
Indeed, the "secret weapon" was the Surströmming that Aomori had obtained from a ten-draw.
Even someone as powerful as Muzan could not be exempted from the effects of the biochemical weapon that is Surströmming.
"What the hell is that?!"
Muzan immediately sealed off his sense of smell, but still felt a momentary dizziness. However, given enough time, he could certainly recover to his original state.
But would Aomori give him that time?
Aomori, whose sense of smell was already sealed, was completely unaffected by the Surströmming. Taking advantage of Muzan's dizziness, he had already reached the Demon King's back, plunging a thin syringe into Muzan's body and injecting all the medication inside.
Then, before Muzan could erupt in fury, Aomori put distance between them.
"Hm?" Muzan felt the injected substance rapidly course through his body. A feeling of weakness emanated from deep within, as large numbers of his cells were killed and destroyed by the substance. He sensed that if he tried to split his body, the separated portions would quickly perish.
"Is it poison? How can there be such a poison?" Aside from the sun, he, Muzan, should fear nothing.
"Surprised? Didn't expect that? That's a friendly greeting from your old friend, Tamayo-san."
By sealing Muzan's ability to split his body, Aomori had finally put the last piece of the puzzle in place for killing the Demon King.
————
You can read the ahead chapter on Patr if you're interested: p-atre-on.c-om/Overgod [Just remove the hyphen to access normally]