"How did humans find this place? Oh, it's that boy Muzan-sama mentioned. How interesting!"
The shoji doors of a room facing Goku's platform slid open. A lean, muscular young man with short, pink hair and dark blue needle-like tattoos etched across his skin stepped out.
Upon seeing Goku, the demon blinked in surprise, which quickly morphed into a look of delighted predatory interest. Muzan had explicitly ordered them: while slaughtering Tokyo, if the Demon Slayer Corps intervened, the boy who killed Rui was to be eliminated first. Any demon who claimed his head would be granted a massive infusion of Muzan's blood.
The demon hadn't expected the boy to show up on his doorstep before nightfall.
"Are you Muzan Kibutsuji?" Goku asked, eyeing the athletic figure.
"Upper Rank Three, Akaza."
The demon introduced himself before blurring into motion. He closed the distance in a heartbeat, his hand reaching out like a claw, intending to simply rip Goku's head from his shoulders. To Akaza, a Lower Rank Five like Rui was a weakling he could crush with a single finger. Even if this boy had killed Rui, he couldn't be much more than a minor nuisance. Only the Hashira truly interested him.
Even then, he had killed so many Hashira over the centuries that even they were beginning to bore him.
However, as he swung his hand with bone-crushing force, he realized he had grabbed nothing but air.
"Eh?"
He spun around to find Goku standing behind him, looking perfectly relaxed.
"It seems you're more capable than I thought." Akaza's eyes lit up with genuine excitement.
Having lost all human memories upon turning into a demon, Akaza lived for one thing: the pursuit of absolute martial perfection. He craved battle with the strong. The speed Goku had just displayed was enough to pique his warrior's spirit.
"Technique Development!"
Akaza slammed his fist onto the floor. A snowflake-shaped compass pattern manifested beneath his feet. This was the core of his Blood Demon Art—a martial arts domain that allowed him to sense an opponent's "Fighting Spirit," predict their movements, and strike at their weaknesses with unerring precision.
"Oh! So you want to duel? Great!"
Goku happily dropped the blue sweater on the ground and fell into the Turtle School's signature fighting stance. If someone wanted to fight him, he wasn't about to say no.
Just then, right next to the blue sweater, a red sweater materialized. In a chaotic blur of motion, a massive contingent of swordsmen appeared on the platform.
The ten seconds were up. Led by the nine Hashira, the elite force of the Demon Slayer Corps had arrived via Portkey.
"What?!"
Akaza reacted instantly, leaping back onto the roof of a nearby floating room to maintain a safe distance. He loved a challenge, but he wasn't a fool. Facing the entire roster of nine Hashira and two hundred elite slayers single-handedly was a death sentence even for an Upper Moon.
...
"Impossible!!"
In the deepest sanctum of the Infinity Castle, Muzan Kibutsuji's eyes snapped open.
Through Akaza's vision, he saw Goku and the two hundred slayers. His mind raced with confusion and disbelief. Not even the Twelve Kizuki could enter this castle unless Nakime summoned them. The fortress was built deep underground with no physical entrances; its location was a secret known only to Muzan.
'Did that brat crack Nakime's spatial barrier?' Muzan's intuition told him this was the work of the boy with the strange powers.
"Nakime! Bring the rest of the Upper Ranks and every demon in the castle to Akaza's location! If they want to die here, we will oblige them!"
His original plan was to lure the Corps to Tokyo. Since they had delivered themselves to his front door, he would crush them here. Naturally, he had no intention of joining the fray himself. If things turned sour, he'd have Nakime teleport him to the other side of the country.
*Bi-ing, bi-ing...*
The haunting sound of a biwa echoed through the shifting halls. In a series of spatial distortions, the other five Upper Moons, the six Lower Moons, and over a thousand lesser demons were instantly repositioned around Akaza.
"It's just as we thought—a spatial Blood Demon Art," Shinobu whispered, drawing her blade.
Facing a literal army of monsters and the terrifying pressure of the Upper Ranks, the slayers didn't flinch. Instead, a fierce, desperate fighting spirit erupted within them. They knew they might be outmatched; they knew they might become food by sunset. But they also knew that if they won today, the thousand-year nightmare would finally end. This was for their families, their fallen friends, and a future where children didn't have to fear the dark.
"How pathetic," Upper Rank One, Kokushibo, muttered. He stared down at the slayers with his six cold eyes, his hand resting on the hilt of his flesh-sword. To him, no swordsman since his brother, Yoriichi, had been worth his time. These "Hashira" were merely ants.
"Such tragic humans," Upper Rank Two, Doma, added with a look of fake pity, waving his golden fans. "Let me save you from your suffering. Come into my stomach and achieve eternal life with me."
The other Upper Moons shared the sentiment. Upper Rank Six alone had killed over twenty Hashira in her lifetime. Why would they fear nine more?
"Hey! Can you tell your boss, Muzan Kibutsuji, to come out? I want to fight him!"
Just as the two armies were about to collide, Goku stepped to the very front. Using a Sonorus charm to amplify his voice, he shouted toward the bridges where the demons were gathered.
His voice boomed through the entire Infinity Castle, reaching even the deepest chambers.