Gyomei Himejima's thunderous blow, fueled by an infinity of grief and a warrior's resolve, screamed through the air.
The Nichirin meteor hammer, wrapped in a tremendous force that tore at the atmosphere, descended on Muzan's face like the judgment of a wrathful god.
The sheer speed and power of the self-sacrificial strike surpassed anything Gyomei had ever unleashed, igniting all the sorrow and rage he felt at his master's sacrifice.
Even the Upper Moons might have been annihilated by such an attack.
But this was Muzan Kibutsuji, the undisputed Demon King.
Though blindsided, Muzan's reaction was inhumanly fast.
He stomped, the ground cracking beneath his feet as he shot backward like a cannonball.
The roaring flail missed his head by a hair's breadth, but the hurricane of force it generated shredded the sleeve of his suit, exposing his arm.
But it wasn't over.
Gyomei would not waste the opportunity his master had paid for with his life.
With a resolute roar, he began to spin, his flail and broad-axe becoming a relentless, alternating storm of destruction that hammered down on the Demon King.
"Stone Breathing, Fourth Form: Volcanic Rock, Rapid Conquest!"
The most destructive of all breathing techniques erupted from Gyomei's body.
The ground shattered under the terrifying bombardment, the sheer force so overwhelming that even Muzan was forced to repeatedly dodge.
"You insect!"
A cold, furious snarl escaped Muzan's lips, his anger mounting at being forced onto the defensive.
Finally, he stopped dodging.
As Gyomei's axe swung in, Muzan raised his exposed right arm to meet it.
"Blood Demon Art: Black Blood Spikes!"
Horrifyingly thick, black blood vessels bulged from his arm before erupting, unleashing a dense thicket of razor-sharp, blood-red thorns.
CRASH!
The sound of metal on demonic flesh was deafening.
A violent shockwave exploded outward, churning up the scorched earth and sending a plume of dust and smoke into the sky.
'So powerful,' Gyomei thought, a grim solemnity on his face as he felt the incredible force transmitted back through his weapon.
The speed and strength of the blood spikes were immense.
He was forced to switch to a defensive posture.
"Stone Breathing, Third Form: Stone Skin!"
The recoil from the clash was so strong that even Gyomei's massive arms trembled violently.
Muzan's scarlet eyes looked on with cold indifference as the Hashira struggled, a cruel arc forming on his lips.
"Is this the full extent of the Demon Slayer Corps' strongest warrior? Truly… disappointing," Muzan taunted, beginning his psychological assault.
"However, if you surrender to me, I can make you the strongest of all demons. Otherwise, you will turn to ash, just like that idiot Kagaya!"
"Dream on!" Gyomei roared. "We do not fear sacrifice!"
"Hmph. Another fool with a rigid mind. Then you can join your dead master in the underworld!"
A flash of madness lit Muzan's eyes as he prepared to overwhelm his opponent.
But in that critical moment, his focus narrowed, his contempt for the Hashira before him causing a fatal lapse in his awareness.
Like two venomous snakes striking from the shadows, two figures launched a silent, perfectly timed attack from impossibly unexpected angles.
One was a purple blur, a butterfly of death moving so fast she was nothing but an afterimage, her entire being radiating the cold fragrance of wisteria.
It was Shinobu Kocho, her demonic transformation pushing her speed beyond its human limits.
"Breath of the Insect, Dance of the Bee Sting: True Thrust!"
Her slender, poison-laced Nichirin blade plunged deep into Muzan's back before he could even register her presence.
"What—?!" Muzan's eyes widened, but it wasn't over.
An even more eerie figure materialized from thin air, a blood-stained talisman on her beautiful, hate-filled face.
It was Tamayo, perfectly concealed by Yushiro's Blood Demon Art until the last possible second.
"MUZAN!" she shrieked, a cry of centuries-old hatred.
Following the path created by Shinobu's blade, she drove her own sharpened claws deep into the Demon King's body.
At that moment, the ultimate payload was delivered.
Shinobu's most potent wisteria concoctions and Tamayo's life's work—a multi-stage, human-reverting drug—were injected directly into Muzan's core.
The timing, the angle, the sheer, suicidal determination—it was a perfect, fatal strike.
For the first time in centuries, Muzan's pupils contracted in something other than anger.
He felt two distinct, deadly threats attacking his very essence.
Tamayo's presence, in particular, had been utterly undetectable.
"Muzan! You will pay for what you've done in hell!" Tamayo screamed, and with a final, resolute act, she broke her own arms, leaving them embedded in his flesh to ensure the full dose was administered.
As one, she and Shinobu launched themselves backward, narrowly avoiding Muzan's furious, reflexive counterattack.
"GUUAAAAARGH! YOU—DAMNED ANTS!"
An earth-shattering roar of pure agony and rage tore from Muzan's throat.
His cells were spinning frantically, trying to break down the alien poisons.
The toxins were splitting and corroding his body from the inside out.
And Tamayo's drug… it was doing something horrifying.
The blood vessels on his skin bulged and writhed like black worms.
His body trembled violently as he felt a sensation he had long forgotten—disgust, and fear.
His cells were being destroyed.
His regeneration was slowing.
And worst of all, some force was trying to pull him back, to revert him to his weak, pathetic… human form.
The enraged Muzan reacted faster than thought.
His back tore open, his suit shredding as dozens of bladed, fleshy whips shot out like striking vipers, lashing toward the retreating figures.
CRACK! CRACK!
Though they dodged desperately, both were caught by the tips of the whips.
Half of Shinobu's arm exploded into a mist of blood as she was sent flying.
Tamayo was slammed to the ground, her own demonic energy flickering.
But it didn't matter.
They had succeeded.
The poison had been delivered.
"BASTARDS!" Muzan's roar shook the battlefield. "I WILL TEAR EACH OF YOU… TO PIECES!"
'Success!'
A flicker of grim joy ignited in Gyomei's heart.
Seizing the opportunity while Muzan was stunned and reeling, he changed his posture, his Nichirin flail roaring as it smashed toward the Demon King's head once more.
The balance of the final battle had been subtly, violently tilted.
But Muzan Kibutsuji's tenacity and terror far exceeded anyone's imagination.
The battle had only just entered its most brutal stage.