Tanjiro and Giyu now stood facing the awakened Muzan. They had reached this place far faster than expected, because Upper Moon Three was already dead. There had been no need to confront him here. Instead, they fought through only scattered demons along the way, arriving without suffering serious injuries.
Around them, the Demon Slayers who were still able to move quickly carried the wounded to safer positions and began treating them. Akira's healing potions proved highly effective. Because of that, the number of casualties was far lower than it should have been in a battle of this scale.
Tanjiro stared at Muzan.
In an instant, his mind flooded with everything that had been taken from him. His family, slaughtered. His sister Nezuko, turned into a demon. Countless Demon Slayers who had fallen along the way. Every tragedy traced back to the man standing before him.
Muzan Kibutsuji.
Tanjiro's body trembled as rage surged through him, threatening to overwhelm his breathing.
"Tanjiro," Giyu's voice cut through the storm in his mind. Calm, steady. "Calm down. Control yourself."
Hearing that voice grounded him. Tanjiro drew a deep breath, forcing the fury back down.
Only then did his shaking finally stop.
Muzan spoke calmly, his voice devoid of emotion.
"Persistent. You are all seriously persistent, and it bores me. It sickens me from the bottom of my heart. Whenever you open your mouths, you only cling to that one foolish notion, avenging your parents, your children, your siblings. You've survived. That should be enough for you."
His eyes remained cold as he continued.
"Your family was slaughtered. What's the problem here? Think of yourself as lucky, and go back to the way you lived before."
Tanjiro stared at him in shock.
"What… what are you saying?"
Muzan answered without hesitation.
"Look at it this way. Being killed by me is the same as encountering a great calamity. You don't need to think so hard about it. Rainstorms. Winds. Volcanic eruptions. Earthquakes. You can't get revenge on a natural disaster, no matter how many lives it takes away."
His voice remained unnervingly composed.
"You can't bring dead humans back to life. So why keep fussing over it? Why not live quietly, earn your daily wages, and accept it? Most humans live that way. Why can't you?"
His gaze sharpened.
"There's only one reason. The Demon Slayers are an assembly of deviants. And I'm tired of dealing with deviants. I'm the one who truly wants to put an end to all of this."
Tanjiro fell silent.
Then, with terrifying calm conviction, he spoke.
"Muzan… you are… a being that should not be allowed to exist."
For a brief moment, everything paused.
Then, without another word, Tanjiro and Giyu lunged forward together, rushing straight toward Muzan.
Muzan's arms twisted grotesquely, flesh stretching and reshaping as they transformed into long whip-like appendages lined with massive, jagged teeth. They lashed out at Tanjiro and Giyu like living cyclones, moving as though they possessed wills of their own.
Tanjiro and Giyu threw everything they had into dodging.
Thanks to their training with Luchan, they were able to keep up with Muzan's attacks far better than they would have in the original story. Even so, Tanjiro could tell immediately, closing the distance was nearly impossible.
If this were before, he would have charged straight in, trusting his instincts. But after being beaten down repeatedly by Akira, or rather, Luchan, he understood now that recklessly closing in would only lead to death.
So instead, he and Giyu focused on evasion, buying time.
It wasn't that they weren't risking their lives. If either of them fell here, everything they had fought for would collapse. And even if they managed to get close, they still couldn't kill Muzan outright.
They had only one option.
Survive until sunrise.
As if sensing their thoughts, Muzan spoke.
"You're buying time, waiting for the sun?"
His lips curled slightly.
"The light won't reach into this fortress. And besides, can you even survive until sunrise?"
Yet beneath his calm exterior, confusion stirred.
Dōma was dead. Kokushibo was occupied elsewhere. And no matter how he tried, he couldn't reach Nakime.
For some reason, Muzan was certain she was still alive. But how had she escaped his control?
The unknown irritated him.
No, more than that, it made him uncomfortable.
He decided there was no need to think further. He would kill these two first, then deal with Nakime himself.
Muzan accelerated.
The storm of attacks intensified, and Tanjiro and Giyu began to struggle. They continued dodging, barely keeping pace.
Then.
Tanjiro's focus wavered for just an instant.
His footing slipped.
"Tanjiro!" Giyu shouted.
Muzan's whip-like hands surged toward him at terrifying speed, and Tanjiro didn't have time to dodge.
But just as the attack was about to hit him,
Something shattered through the floor above Muzan.
No, someone.
Jet-black armor tore through the ceiling, glowing purple lines blazing like constellations across its surface.
Akira had arrived.
The moment he broke through the floor, he attacked without hesitation.
"Falcon Kick."
A flaming dropkick slammed directly into Muzan.
The impact obliterated the wooden floor beneath them. Both bodies crashed downward, through one floor, then another, and another, until Akira kicked Muzan away mid-fall, sending him flying across the chamber. Muzan smashed into a distant wall, the structure cracking from the force.
Akira landed smoothly and looked up.
"Hey, Muzan. Seems like you're still alive."
Muzan rose from the rubble, his body already fully healed. Hatred seeped into his voice as he muttered,
"…Hoshino Akira."
Akira tilted his head slightly.
"Are you prepared for your retribution?"
Muzan sneered.
"You think you can beat me? The tricks you used on Akaza won't work on me."
"Probably," Akira replied calmly. "But I have more tricks than you think."
As he spoke, two Nichirin blades materialized in his hands.
Akira drew a breath.
Star Breathing activated.
Both blades ignited with a brilliant purple glow, light rippling along their edges as power surged outward.
Muzan stared at the glowing blades in shock.
"…What is that?"
Inside his mind, an old memory surfaced, of a swordsman from the past, one who had nearly pushed him to the brink of death. That blade had glowed red.
This one glowed purple.
And it felt far more dangerous.
Muzan attacked first.
His arms twisted and elongated, transforming into long, flesh-made whips lined with massive, jagged teeth. They lashed out at Akira at terrifying speed, striking like a cyclone driven by pure killing intent.
Akira didn't retreat.
He casually swung his sword.
One of Muzan's whip-arms was severed cleanly, cut apart like butter under a hot knife.
Muzan froze.
He hadn't expected it to be that easy.
Then the pain hit.
The moment the glowing purple blade sliced through him, agony unlike anything he had felt before tore through his body. It burned deeper than Nichirin steel, deeper than sunlight-adjacent attacks. Muzan clenched his teeth and endured it, but his shock was undeniable.
Akira looked at him calmly.
"What do you think of this trick, Muzan?"
Muzan's expression twisted in anger.
He understood now, those swords were dangerous.
Deciding not to hold back any longer, Muzan unleashed his full power.
From his back, nine whip-like extensions burst forth, each one sharp, reinforced, and overflowing with lethal force. His legs shifted grotesquely, reshaping themselves into limbs built for explosive speed and massive jumping power.
All of his whips struck at once.
A storm of attacks descended on Akira from every direction.
Akira didn't dodge.
He didn't block.
He simply walked forward.
Every one of Muzan's attacks crashed against Akira's Eclipse Armor and failed to penetrate it.
Muzan screamed.
"WHAT?!"
Akira kept advancing.
"I told you, didn't I?" he said evenly. "I am your divine retribution."
Panic crept into Muzan's mind.
He couldn't break the armor.
He couldn't figure out how to hurt him.
In truth, Akira's armor was getting weaker than before, but because it was his Device, it would not shatter so easily.
Akira swung his sword again.
Several of Muzan's tentacles were severed at once. They began regenerating, but far more slowly than before.
Muzan realized it then.
If he continued fighting like this.
He would lose.
So Muzan used a powerful technique he always uses when he was pushed to the limit, it was the Jostar family secret technique.
He ran.
Akira didn't allow him to escape so easily.
He chased Muzan relentlessly, but Muzan was fast, far faster than most demons. He tore through the twisting corridors of the Infinity Castle and arrived at the very place where he had slaughtered the Demon Slayers earlier.
Blood still stained the floor.
Without hesitation, Muzan's whip-like tentacles extended outward and snatched up the Nichirin blades scattered across the ground, the swords of the fallen.
He knew using them was beneath him.
But he also knew he couldn't continue fighting Akira's purple blades barehanded.
Akira arrived moments later and took in the sight.
"Oh," he said calmly, "that's not a bad idea."
Now armed with multiple Nichirin swords, Muzan attacked.
His tentacles whipped violently, swinging the blades like a hurricane, an overwhelming storm of steel and killing intent.
By then, Tanjiro, Giyu, Obanai, and Mitsuri had also reached the battlefield. Tanjiro clenched his teeth in rage as he watched Muzan wield the weapons of fallen Demon Slayers so casually.
Akira didn't hesitate.
He rushed straight into the storm of attacks.
Because Muzan was now using Nichirin blades instead of organic whips, he could finally block Akira's glowing purple swords. Akira was forced to block or dodge in response, steel clashing against steel.
But with the Transparent World, Akira could see everything.
Every angle.
Every movement.
Every opening.
He countered effortlessly, dodging and deflecting while steadily closing the distance.
As he fought, Akira observed Muzan's internal structure clearly.
"Seven hearts. Five brains. If I destroyed all of them, would Muzan die?"
Akira wasn't certain.
But it was worth testing.
At that moment, the others attacked as well, three Hashira and Tanjiro striking Muzan from multiple directions. Their assault forced Muzan to divide his attention, giving Akira the opening he needed.
Akira closed in.
"Star Breathing—First Form: Flashing Comet."
Like a streak of light, he cut through Muzan's arm, and destroyed one of his brains.
Muzan panicked and attempted to split his body apart, just as he had done long ago when fighting Yoriichi.
But nothing happened.
He couldn't divide.
"What? Can't divide and escape?" Akira spoke calmly as his blade moved again. "Might I remind you of the poisons you absorbed, one of them prevents division."
Muzan's eyes widened in realization.
"You...."
Akira didn't stop.
Another slash, another brain destroyed.
Then a heart.
Then another brain.
Muzan's attacks failed to injure Akira at all, blocked entirely by the Eclipse Armor. Akira continued cutting him down relentlessly, destroying hearts and brains one after another.
Muzan panicked.
He tried to flee again.
Akira didn't let him.
He attacked again and again, and just as he was about to destroy the final brain.
Akira's Device, Eclipse, suddenly unsummoned.
Akira froze.
His hands were suddenly empty.
The Eclipse armor that's covering him was gone.
For a split second, disbelief crossed his mind.
"What the hell...?"
That instant was all Muzan needed.
Every mouth across Muzan's twisted body opened at once.
A deafening roar erupted as a massive shockwave of compressed energy exploded outward, slamming directly into Akira. The impact tore through him, violently disrupting his nervous system. His body spasmed as pain unlike anything before coursed through every nerve.
He couldn't move.
Before he could recover.
Muzan's tentacle whips lashed out.
They tore through Akira's body in a brutal storm of slashes. Flesh split. Blood sprayed across the shattered floor, scattering in every direction.
Akira was cut down.
Blood splattered everywhere.
From the edge of the battlefield, Tanjiro saw it.
His eyes widened in horror.
"AKIRA-SAN!"
His scream echoed through the Infinity Castle.