Chapter 16: A New Threat in the Shadows
With Muzan punted into the sun and the demons seemingly defeated, the Demon Slayer Corps entered a state of uncertain peace.
For the first time, the Hashira could actually relax.
Or so they thought.
---
Breakfast at the Butterfly Estate
The morning after Saitama's "battle," the Hashira and Tanjiro's group gathered in the dining hall for breakfast. Plates of rice, miso soup, grilled fish, and pickled vegetables filled the table.
"Man, this is nice," Saitama said, shoveling rice into his mouth. "No demon attacks, no screaming, just food."
"You really are incredible, Saitama-san," Kanao said softly, still a bit stunned by how casually he ended centuries of war.
"Well, it's not a big deal." Saitama scratched his cheek. "I just punched stuff."
Tengen clapped his hands loudly. "Let's toast to our new Bald Savior!"
"Stop calling me that."
Everyone laughed. Even Sanemi managed a rare grin. For the first time, the tension that had hung over the Corps for generations seemed gone.
---
Deep Underground
Far beneath the surface, hidden in a forgotten chamber, something stirred.
A hand, ancient and shriveled, slowly reached out from a pool of black liquid. Its nails were long, jagged, and dripping with blood.
In the dim light, two glowing red eyes snapped open.
"So… Muzan has fallen."
The voice was neither male nor female — it was something far older. Something that had existed before even Muzan himself.
---
Demon Slayer HQ
At the same time, Oyakata-sama (Kagaya Ubuyashiki's successor) summoned all the Hashira for a sudden meeting.
"I know you all believe the war is over," he began, voice calm but serious. "However, our crows have detected strange movements in regions once controlled by demons. A new presence has emerged."
"Another demon?" Giyu asked, frowning.
"We're not sure," Kagaya's successor replied. "But the aura is far stronger than any Upper Moon we've recorded — including Muzan himself."
The room fell into stunned silence.
"How is that possible?" Shinobu asked. "Muzan was the progenitor. There can't be anyone stronger than him!"
"That's what we thought," the new leader said. "But… there's something the records don't mention."
He opened an ancient scroll, written in trembling ink.
"This speaks of a demon so powerful that even Muzan feared it. A being known only as Upper Moon Zero."
---
Who is Upper Moon Zero?
Long before Muzan became the Demon King, there was a myth among demons.
A creature born not from Muzan's blood, but from the blood of something even more ancient — a being directly connected to the origins of all curses and demons in Japan.
This creature, unlike the others, slept for centuries, unconcerned with Muzan's ambitions.
Until now.
With Muzan gone, the seal binding Upper Moon Zero began to weaken.
---
Saitama's Reaction
"Okay, and?" Saitama asked, halfway through his third bowl of rice.
Everyone stared at him.
"Did you not hear?! This thing is even stronger than Muzan!" Zenitsu cried.
"So?" Saitama blinked. "If it's evil, I'll just punch it."
"Stop saying it like that solves everything!" Shinobu sighed.
"But it does," Inosuke grinned. "That's what makes him awesome!"
---
A Sudden Attack
Before the meeting could continue, the walls trembled. A dark mist poured through the windows, chilling the air.
Everyone drew their swords.
From the mist, a figure emerged — tall, cloaked in tattered black robes, its face hidden by a featureless white mask. Its aura was wrong, unlike any demon they had fought before.
Saitama slurped the last of his soup. "Oh, is this the new guy?"
The figure raised a single hand, and every Hashira collapsed to their knees — their bodies crushed under some invisible pressure.
"What… is this…" Mitsuri gasped, struggling to breathe.
Only Saitama stood unaffected, scratching his head. "Huh. Neat trick."
The figure spoke, its voice echoing from everywhere and nowhere.
"I am the shadow that even Muzan feared. I am Upper Moon Zero, the First Curse."
"Cool." Saitama cracked his knuckles. "Want to fight?"
---
End of Chapter 16