Kibutsuji Muzan could feel an aura that filled him with indescribable fear. He stared in terror at Kokushibō, whose entire body was now burning with flames.
"Tsugikuni Yoriichi?! No… Kokushibō—how could you possibly have mastered the Breath of the Sun?!"
"I am Tsugikuni Michikatsu. I am no longer Kokushibō! Kibutsuji Muzan—this ends with me stopping you!"
In his hand, Michikatsu held the demonic blade forged from his own flesh and blood. As the flames consumed its living tissue, the sword's true form as a samurai katana was revealed.
Muzan gnashed his teeth in rage. The demon he had created had somehow broken free of his curse—and even more impossibly, had awakened the Breath of the Sun, the ultimate power that was the natural enemy of all demons.
At this moment, Michikatsu activated his Mark and entered the Transparent World. He could see everything—Muzan's lungs expanding and contracting, the pulse of his veins, the flow of his blood.
Through the Transparent World, Michikatsu discovered Muzan's weakness—five brains and seven hearts hidden within his body. Only a crimson blade, imbued with the same power as sunlight and wielded through the forms of the Breath of the Sun, could strike those twelve vital points and destroy his so-called immortality.
Michikatsu tightened his grip with immense strength, turning his blade crimson as he murmured softly,
"Let's go… Yoriichi."
"Breath of the Sun, Seventh Form: Setting Sun Transformation!"
In an instant, Michikatsu flashed into the air, his blade wrapped in flames as dazzling as the sun itself. Inverted mid-air, he swung down in a blazing horizontal slash toward Muzan.
Sensing the danger, Muzan did not dare to underestimate him. He instantly entered his Demon King form—his jet-black hair turned deathly white, his limbs and lower body were wrapped in blood and hair, and his entire body sprouted gaping maws lined with fangs.
Nine whip-like tentacles burst from Muzan's back, lashing toward Michikatsu in midair at incredible speed.
Facing the onslaught, Michikatsu cut through the whips with Setting Sun Transformation, ending the form's motion.
Although he had awakened the Breath of the Sun, centuries had passed since his time as a human. He had never once practiced it—his mastery, attunement, and control were all incomplete.
And the flames of the Breath of the Sun burned him as well. Michikatsu could feel the fire searing his demonic flesh. He knew his time using this technique was short. He had to deal a decisive blow to Muzan before the flames consumed him.
At that moment, Dōma, Hantengu, and Kaigaku stepped forward, blocking his path.
"Breath of the Sun, Fifth Form: Solar Radiance Thrust!"
Michikatsu raised his crimson blade horizontally, piercing straight past the three demons toward Muzan.
"Blood Demon Art: Frozen Cloud!"
Dōma swept his twin fans, filling the air with shimmering ice crystals that surged toward Michikatsu like a blizzard.
From behind, Hantengu's strongest clone, Zohakuten, emerged.
"Blood Demon Art: Infinite Tree Barrage!"
Zohakuten struck the drums on his back, summoning colossal wooden dragons that twisted and roared, sweeping toward Michikatsu with crushing force.
"Breath of Thunder, Fifth Form: Scorching Realm Lightning!"
Kaigaku unleashed lightning wreathed in intense heat—once golden, now a sinister black due to his transformation into a demon.
"Moon Breathing, Fifth Form: Moon Spirit Calamity Vortex!"
Michikatsu invoked a defensive technique without even drawing back his blade. A massive vortex of slicing wind encircled him, accompanied by countless crescent-shaped blades.
As one of the original Breathing Styles, the Breath of the Moon now intertwined perfectly with the Breath of the Sun—unlike Tanjiro, Michikatsu suffered no backlash from the simultaneous use.
The crescent blades, once glowing like moonlight, now shone like the blazing sun itself, deflecting every incoming attack as Michikatsu drove straight toward Muzan.
Muzan's eight leg-whips moved even faster than the nine from his upper body, their velocity breaking the sound barrier as they shot toward Michikatsu.
"Breath of the Sun, Seventh Form: Fake Rainbow"
Michikatsu twisted and spun at blinding speed, his body flickering in and out of sight. To Muzan's eyes, he was nothing but afterimages.
"Breath of the Sun, Eighth Form: Flying Flame Wheel!"
As he closed in, Michikatsu's blade wavered like a heat haze, creating the illusion of shortening. He thrust toward one of Muzan's internal brains hidden within his chest.
Muzan felt a sudden, stabbing pain—at that instant, the blade returned to full length, piercing through and destroying the brain in his chest.
"Muzan-sama!"
Dōma, Hantengu, and Kaigaku cried out in horror. Despite their combined assault, Michikatsu had broken through their defense and struck Muzan directly.
Enraged, Muzan unleashed a massive shockwave, blasting Michikatsu backward.
Clutching his wounded chest, Muzan's fury gave way to a twisted smile.
"So that's it, Kokushibō. I don't know how you managed to grasp the Breath of the Sun, but you are not that man. Compared to his flames, yours are pitifully weak!"
He remembered the day he fought Tsugikuni Yoriichi—when Yoriichi's blade had sliced his shoulder. The searing flame that clung to the wound never faded; even when he tore away the burning flesh, the scar remained, unhealable for eternity.
Michikatsu's flame burned with the same quality—but far weaker. Though it caused agony, it lacked that inexorable, bone-deep fire. The wound could still slowly regenerate.
Muzan looked down contemptuously at the panting Michikatsu.
"I'm guessing your time using the Breath of the Sun is limited. The very flames you wield are consuming you from within."
Muzan's guess was correct. The balance between flame and regeneration was fragile. Each use of a Sun Breathing form made the flames burn hotter, tipping that balance.
If Michikatsu continued to fight like this, he would turn to ash before the battle's end.
As the fight dragged on, his strength would only diminish further.
Meanwhile—
Having just returned to the Butterfly Estate from the ruins of the Ubuyashiki residence, Yōsuke had planned to calm himself. But under the moonlight, he saw a familiar figure.
He called out cautiously,
"Yoriichi?"
Tsugikuni Yoriichi looked sorrowful as he bowed his head and spoke softly,
"Yōsuke, I have a request to ask of you."
Yōsuke frowned in confusion.
"What is it?"
"My elder brother is now fighting a desperate battle against Kibutsuji Muzan on Nakime's island. Please… help him. This is my final request."