For a brief instant, the night was swallowed by fire.
The entire Ubuyashiki mansion vanished in a catastrophic explosion, flames tearing through the darkness as if the world itself had been ignited. This was no ordinary blast. It was far greater than the one recorded in history, far greater than anything seen in the original events.
After all, this explosion had been designed by Akira.
And according to him, the bigger the explosion, the better.
The mansion was erased completely, reduced to nothing but fire and debris.
From the heart of the inferno, Muzan Kibutsuji's body was hurled outward.
What remained of it, anyway.
All four limbs were gone. Most of his torso had been obliterated. Even his head was barely intact. Yet, despite that, his flesh began to wriggle and crawl back together.
Slowly.
Very slowly.
"That madman…" Muzan's thoughts churned as his regeneration struggled to keep pace. "I expected a trap. I expected poison, sacrifice, ambush… but blowing himself up?"
His eyes narrowed as fragments of his body pulled themselves together.
"Is he even dead? No… I felt something when we exploded."
As Muzan regenerated, his confusion deepened.
"If he survived that… then what in the world even is he?"
There had been something deeply unsettling about that boy.
"I couldn't sense even a trace of malice from him. No hatred. No fear. Only curiosity."
Even in the moment of detonation, there had been no panic. No killing intent. Just calm interest, as if he were observing an experiment rather than standing at the center of his own death.
Muzan's legs finally reformed, allowing him to stand.
That was when he noticed it.
The remnants of the explosion weren't ordinary debris.
Tiny caltrops, countless microscopic shards, were embedded throughout his body, tearing at newly formed flesh each time it tried to regenerate.
"So that's it…" His regeneration slowed even further. "They were designed to delay me. To buy time."
Which meant only one thing.
"There's more coming."
His gaze sharpened.
"That boy has another plan already in motion."
Was it the Hashira?
No.
Something about this felt different.
"Then what… what is it?"
As that thought crossed his mind, something strange appeared.
Floating silently around him, glowing seeds of blood emerged one by one, hovering in the air like ominous embers.
Muzan stared at the floating crimson lights.
"Seeds of blood…?"
His instincts screamed in warning.
"Is this a Blood Demon Art?…but whose?"
Before he could analyze further, the seeds burst open.
In an instant, gigantic blood spikes erupted outward, exploding in every direction like blooming crimson thorns. They pierced straight through Muzan's body, arms, torso, and legs, skewering him in place.
And it didn't end there.
Once inside his flesh, the spikes continued to branch, splitting again and again into smaller, sharper offshoots. They spread throughout his body, weaving through muscle and bone like parasitic roots.
More.
And more.
And more.
For the first time in centuries, Muzan Kibutsuji was restrained.
At least, for a while.
Instinctively, Muzan began to absorb the foreign blood, even as his thoughts raced.
"Who is it?Who dared do this to me?"
Then.
He sensed it.
Muzan turned his gaze sharply.
Not far away stood a blonde-haired girl with blue eyes, one hand raised as blood shimmered around her.
He recognized her immediately.
"That girl…"
She was the same one who defeated Hantengu before and also used Blood Demon Arts before.
And yet.
"She is neither demon nor human."
He had intended to capture her once.
Now, she was using that same power to bind him.
Muzan's expression darkened.
"Black Blood Brambles."
At his command, black blood erupted from his hand, twisting and writhing before transforming into jagged, thorned brambles. They lashed forward, tearing through the air toward Erika.
But before they could reach her.
A black figure moved.
Something rushed in from the side, placing itself directly between Erika and the attack.
The brambles struck.
And dispersed.
They shattered harmlessly against the surface of jet-black armor, dissolving as if they had hit an immovable wall. Not a single scratch was left behind.
Not even a mark.
Muzan's eyes narrowed.
Yes, It was Akira.
The black figure standing before Muzan was none other than Hoshino Akira, his Eclipse Armor fully summoned at last, for an actual battle in this world.
Erika snapped sharply, her voice cutting through the chaos.
"Where were you?! You were supposed to help me attack him!"
Akira tilted his head slightly. "I'm sorry. I didn't expect the explosion to send me flying into the forest."
Erika glared. "That's why I told you standing inside an exploding building was dangerous."
Akira shrugged, utterly unapologetic.
"Well, I had to be the bait. And it looked cool."
Yes.
Akira had summoned his armor the instant the explosion went off, allowing him to survive without issue, but the sheer force of the blast had sent him hurtling through the forest.
For dramatic effect, he had been standing on top of a massive bomb when it detonated.
Purely to look cool.
Muzan listened to their exchange and finally understood.
The black-armored figure standing before him…
"…So you're alive," Muzan said coldly. "Hoshino Akira."
Akira nodded casually.
"Yeah. An explosion of this level can't kill me."
Then, as if noticing something amusing, his gaze shifted.
"Oh," he added. "You've already absorbed quite a lot of those blood spikes. Good. Very good."
He turned his head slightly.
"Erika, can you add more?"
Erika sighed, clearly annoyed by his earlier stunt, but she complied.
Raising her hand, she reached into her inventory.
In the air around Muzan, new glowing blood seeds appeared, hovering for a split second.
Then they detonated.
Once again, enormous blood spikes erupted outward, stabbing into Muzan's body from every direction, reinforcing the restraints and flooding his system with more foreign blood.
Muzan's expression finally shifted.
Something was wrong.
As he absorbed the blood, he felt it.
"I'm… getting weaker?"
His instincts screamed.
"What is this?" Muzan demanded, even as he continued absorbing the spikes.
Akira answered calmly.
"Oh, these? This is a Blood Demon Art Erika learned from the man you turned into a demon in Asakusa, to escape Tanjiro."
He paused, eyes glowing faintly behind the armor.
"But these ones are a bit special, you know."
Muzan's gaze sharpened.
"…What do you mean?"
Even as he asked, he continued trying to absorb more of the spikes, unaware of just how deep the trap had already sunk into him.
Akira continued calmly, as if explaining a simple experiment.
"These ones contain a lot of poisons that are bad for demons," he said with a smirk, "and even a medicine that can turn a demon back into a human."
Muzan's eyes widened slightly.
"That's impossible," he said coldly. "Such a thing doesn't exist."
Akira tilted his head.
"It didn't before," he replied. "But it does now."
Muzan's expression twisted.
"Even if it exists," he said, "how could a Blood Demon Art withstand something like that?"
Akira answered without hesitation.
"That's because Erika isn't a demon," he said. "And her Blood Demon Art isn't an actual Blood Demon Art."
He raised a finger slightly, as if lecturing.
"It's just a specialized form of blood manipulation. So it won't be affected."
Yes, this was all part of Akira's master plan.
First, he had used himself and the Blue Spider Lily as bait instead of the Ubuyashiki family.
And now, he had used this method to ensure that Tamayo wouldn't have to die for the sacrificial plan either.
The blood seeds floating around Muzan were mixed with every poison and medicine that Akira, Tamayo, and Shinobu had created together.
Erika's newly developed blood manipulation made this possible.
And the blood itself.
It belonged to Sanemi.
Since his blood was known to be especially appealing to demons, it made the perfect carrier.
Absorbing Akira's or Erika's blood would have been far too dangerous.
That was why the blood seeds had been stored safely inside the inventory instead.
Erika didn't want to drink anyone else's blood, after all, so she carried the seeds in her inventory.
As Muzan processed everything Akira said, shock and fury twisted his expression.
But Akira wasn't finished.
"Oh, come on," he said lightly. "This isn't even my final gift for you."
Muzan's eyes snapped toward him.
"…What?"
At that exact moment.
CRASH.
Muzan's head was completely smashed apart by a massive spiked flail, exploding into fragments.
The force shook the ground.
Yes.
The Stone Hashira had arrived.
But Muzan's destroyed head regenerated instantly.
Flesh twisted, bones reformed, and in the span of a breath, his face was whole again, cold, furious, and intact.
At that exact moment, footsteps thundered in from every direction.
The Hashira arrived.
Along with them came Tanjiro.
"OYAKATA-SAMA!"
Their voices overlapped, raw with panic and disbelief as they stared at the ruins of the Ubuyashiki mansion, nothing but scorched earth, shattered wood, and lingering flames.
Shock rippled through them.
Akira watched from where he stood and thought calmly,
"Oh yeah… they were all kept in the dark."
No one knew the real plan.
Every single one of them believed their Oyakata-sama was dead.
That had been Kagaya's decision, to ignite their grief, to sharpen it into rage, to turn despair into resolve.
Just as he had intended.
Then the Stone Hashira roared, his voice shaking the battlefield.
"IT'S MUZAN! KIBUTSUJI MUZAN IS HERE! He won't die even if you cut off his head!"
The shock shattered.
And in its place.
Rage erupted.
Tanjiro's eyes burned as he screamed the name carved into his soul.
"MUZAN!"
He drew his Nichirin blade and charged without hesitation.
Not just him.
Every Hashira surged forward at once, Breathing Styles igniting in full power.
"Mist Breathing, Fourth Form!"
"Insect Breathing—Butterfly Dance!"
"Serpent Breathing, First Form!"
"Love Breathing, Fifth Form!"
"Flame Breathing, First Form!"
"Sound Breathing, First Form!"
"Water Breathing, Third Form!"
"Wind Breathing, Seventh Form!"
And.
"Hinokami Kagura—Sunflower Thrust!"
Blades flashed.
Techniques unleashed.
All of them rushed toward Muzan at once, unleashing everything they had, every ounce of fury, grief, and hatred, as the battle against the Demon King truly began.
Muzan smirked.
And in that instant, the ground beneath everyone vanished.
The earth split apart, replaced by massive Japanese sliding doors opening wide beneath their feet.
There was no time to react.
Tanjiro, the Hashira, and everyone fell.
They plunged downward, swallowed by a world that should not exist.
What awaited them below was a realm of impossible architecture.
Endless corridors twisted in every direction.
Gravity inverted without warning.
Walls folded into ceilings, ceilings became floors, and space itself bent and shifted as though mocking logic.
A castle that defied reason.
A labyrinth that lived and breathed.
It was.
The Infinity Castle.
Akira, Erika, all the Hashira, and Tanjiro were dragged into it.
And not just them.
Across the entire region, every single Demon Slayer felt the ground beneath their feet open. One by one, trap doors yawned wide, and all of them fell, swallowed by the endlessly shifting, infinite castle.
The battlefield was scattered.
The war was separated.
As the world spun and reassembled itself mid-fall, Akira twisted his body and landed cleanly on a floating platform.
And there.
Standing not far from him.
Was Muzan.
Muzan laughed.
It was a vicious, echoing sound that twisted through the impossible space of the castle.
"Do you think you've got me cornered?" he sneered.
"You are all going to hell. The Demon Slayers are an eyesore tonight. All of you will be trapped in here, and I am going to slaughter every last one of you."
Akira smirked. "Hey, I'm not trapped in here with you."
He lifted his gaze, purple eyes glowing faintly.
"You're trapped in here with me. No matter how big this place is, I will find you and kill you. So be sure to survive until then, Kibutsuji Muzan."
Muzan's expression twisted into pure, murderous rage.
"Do it if you can," he snarled. "Hoshino Akira."
A sharp biwa note rang out.
The platform beneath Akira shifted, transforming instantly into an open door.
The floor vanished.
Akira fell.
As he dropped into the depths of the Infinity Castle, he caught one last glimpse of Muzan, still struggling, still trying to absorb the remaining blood spikes embedded in his body.
As the darkness swallowed him, Akira turned his head slightly, eyes calm even as he fell.
"Well then," he said quietly but with excitement in his voice,
"The game begins now."