Chapter 17: The First Curse vs The One Punch Man
The room shook as Upper Moon Zero's presence thickened like a fog, pressing down on the Hashira until their limbs felt like lead.
Even Gyomei, the strongest Hashira, was gritting his teeth, veins bulging as he struggled to hold his stance.
"This isn't just Blood Demon Art," Shinobu wheezed, sweat dripping down her forehead. "This is… ancient."
Upper Moon Zero's mask cracked slightly, revealing just the corner of a mouth — curved into something that wasn't a smile but something far more unsettling.
"Bow," the demon whispered.
The Hashira collapsed entirely, unable to resist. Only Tanjiro, Nezuko, and Saitama remained standing — Tanjiro trembling, Nezuko's demon side raging to fight back.
Saitama, on the other hand, scratched his ear. "Huh? What's everyone doing on the floor?"
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A Presence Beyond Logic
Upper Moon Zero tilted its head, clearly confused. "You are… unaffected?"
"Yeah, I guess." Saitama shrugged. "I'm built different."
"Your existence is an anomaly, even to me." The demon's voice echoed with curiosity, but also caution. "What are you?"
"Just a guy who's a hero for fun."
Upper Moon Zero's aura flared, cracks splitting across the walls and floor. The sheer pressure ripped apart the roof of the building, sending debris flying into the sky.
Saitama caught a falling roof beam with two fingers and set it aside casually. "Hey, that's dangerous, you know."
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The First Strike
Without warning, Upper Moon Zero moved. No sound. No blur. Just gone—and suddenly right in front of Saitama, a black claw slicing toward his neck.
SMACK!
Saitama slapped the claw away with the back of his hand like he was swatting a mosquito. The force of that single slap shattered the ground beneath them, sending a shockwave that uprooted trees and blasted the mist away for kilometers.
Upper Moon Zero stumbled back, its entire arm missing.
The demon froze. Even Muzan, in his prime, wouldn't have reacted that fast—let alone with such ridiculous strength.
"What… are you?" Upper Moon Zero's voice cracked for the first time, tinged with genuine fear.
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Tanjiro's Breath of the Sun
"Tanjiro, now!" Saitama called.
"Huh? What do you mean now?! I can't—"
"Just swing your sword real flashy. I'll do the rest."
Tanjiro took a deep breath, channeling Breath of the Sun, flames dancing along his blade.
"Hinokami Kagura: Flame Dance!"
He slashed toward Upper Moon Zero, who raised a second arm to block — only for Saitama to flick Tanjiro's blade mid-swing, accelerating it faster than sound.
The blade sliced clean through the demon's chest, flames exploding outward.
"Aghhh—!" Upper Moon Zero howled, falling back. Its flesh refused to regenerate.
"Demon Slayer blades can't harm me like this—"
Saitama held up a single bottle of cooking oil.
"Found this in the kitchen."
He poured it over Tanjiro's blade. The flames intensified unnaturally, glowing almost white-hot.
"Flaming oil blade. I saw it in a cooking manga once," Saitama said proudly.
"That's not how swords work!" Shinobu screamed from the floor.
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Upper Moon Zero's True Form
The ancient demon roared, its mask fully shattering as its body expanded into something grotesque — a mass of writhing flesh, eyes, and mouths, all chanting in a language no one understood.
Nezuko transformed, her own demonic power rising to match the threat.
But Saitama sighed. "Ugh, it's always the same."
He stepped forward, raised a single fist, and punched.
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Serious Punch
There was no wind-up. No technique. Just a simple straight punch aimed at Upper Moon Zero's core.
BOOOOM!
The punch landed.
The earth split apart for ten kilometers, the sky rippled like a stone thrown into water, and every tree in a radius disintegrated into splinters.
Upper Moon Zero didn't even have time to scream. It just ceased to exist—every cell erased before its ancient power could even retaliate.
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Silence
The dust settled. The Hashira, now freed from the crushing pressure, slowly sat up in stunned silence.
"Is… is it over?" Mitsuri whispered.
Saitama shook his head. "Nah, probably not."
"Why?!" Sanemi shouted. "You just punched that thing out of existence!"
Saitama scratched his cheek. "Yeah, but these stories always have some hidden boss or secret revenge plot, right?"
Zenitsu fainted.
Tanjiro just smiled weakly. "Thank you, Saitama-san."
"No problem."
"Also…" Saitama glanced down. "Can I have more rice? I'm still hungry."
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The Calm After
The sky cleared. The mist was gone.
For now, the Demon Slayer Corps had won again, thanks to a bald hero who just wanted lunch.
But deep in the forgotten lands, far beyond the reach of human knowledge, a new set of eyes opened — eyes belonging to something even older than Upper Moon Zero.
The story wasn't over yet.
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End of Chapter 17