Chapter 20: Abyssal Moon Zero vs Saitama
The air was heavy. The sky above the Moonlit Valley darkened unnaturally, even though the sun hadn't set. A ring of crimson light circled the sky like an eclipse frozen in time.
Tanjiro's breathing was uneven—not from exhaustion, but from sheer pressure radiating off the figure standing before them. Even Nezuko, safe within her box, stirred restlessly, sensing the ancient malice filling the air.
Abyssal Moon Zero stood at the edge of the battlefield, his tattered bandages fluttering as though the wind itself feared touching him. His hands were stained black, fingertips dripping with a substance darker than ink. His presence wasn't just intimidating—it felt wrong, like reality itself was rejecting his existence.
"You… are no ordinary Demon Slayer," Zero said, his eyes settling on Saitama. "Nor are you a demon. What are you, bald man?"
Saitama scratched his ear lazily. "Just a guy who's a hero for fun."
There was silence. No one knew how to react to that, not even the ancient Abyssal Moon.
"Are you mocking me?" Zero's voice was low, but the fury in it shook the ground. Cracks spiderwebbed across the valley floor, releasing tendrils of cursed energy that snaked toward Saitama's feet.
Saitama yawned. "Not really. I'm just here 'cause I heard there was a strong guy. Are you strong?"
Zero raised his hand, fingers curling like a claw. The shadows at his feet came alive, forming into a massive beast with countless mouths, each one chanting ancient curses that burned the air itself.
"Test me," Zero said.
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Instant Chaos
Before Tanjiro or the others could react, Zero's shadow beast lunged, a maelstrom of teeth and claws aiming directly for Saitama. The ground beneath Saitama exploded from the force of the creature's speed.
Saitama didn't move. He simply extended his fist and—
BOOM
With a single, casual punch, the entire shadow beast vaporized, leaving behind only a faint echo of its curse. The impact blew a crater into the ground 50 meters wide, sending rocks and debris flying into the sky.
Everyone stared. Even Inosuke, who always acted like he wasn't scared of anything, took a step back.
"What the hell is that bald dude?!" Zenitsu screeched.
Zero's glowing eyes narrowed. "Interesting."
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A Moon's Wrath
Without warning, the bandages around Zero unraveled, revealing his true form. His skin was made of obsidian flesh, carved with thousands of cursed sigils that constantly shifted like living ink. His arms split into six, each one holding a different weapon forged from darkness itself—a spear, a scythe, a bow, a blade, a whip, and a staff.
With a single motion, Zero unleashed a barrage of attacks. Blades of shadow, arrows of cursed flame, tendrils of void—all of it converged on Saitama at once, blotting out the sky.
"Serious punch."
Saitama swung his fist once.
The air itself split apart, creating a shockwave so powerful that every attack disintegrated before it could even touch him. The force continued, blowing away the mist, the ruins, even the clouds above. For a brief moment, the night sky turned clear and bright, as if nature itself was terrified to get in the way.
Zero staggered back, his obsidian skin cracking. "Impossible."
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Demon Slayers Join In
"Let's go!" Tanjiro yelled, snapping out of his shock. "Saitama-san opened a path!"
"Thunder Breathing: Seventh Form!" Zenitsu blurred into motion, lightning crackling around him as he targeted Zero's legs.
"Beast Breathing: Dual Fang Frenzy!" Inosuke spun into the fight, his dual blades carving through the lingering shadows trying to reform.
"Hinokami Kagura: Dance of the Solar Tempest!" Tanjiro's flaming blade swept through the air, flames licking at Zero's cursed skin, preventing his regeneration from activating.
Even Shinobu, watching from the sidelines, loaded her sword with a specialized venom—a new poison crafted specifically for these ancient demons.
"Let's see how you handle wisteria infused with purified sunlight," she whispered, launching herself into the fight.
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Zero's Last Stand
Despite their combined assault, Zero's strength was far above any Upper Moon they had faced before. Even with his body cracking under Saitama's blows, his curses began to weave into reality itself, twisting the battlefield into a realm where pain became power.
"Even if you break me," Zero hissed, "I will simply become part of the world itself."
Saitama shrugged. "That sounds annoying."
He cracked his knuckles.
"Guess I'll just punch the whole world if I have to."
With that, Saitama leapt into the air—higher than anyone could see, breaking through the cursed sky itself. For a moment, all they saw was a small dot.
Then, he descended—fist first, aimed directly at Zero's heart.
"Serious Series: Abyss Breaker Punch!"
The moment his fist connected, everything froze—time itself stuttering from the sheer force.
The ground shattered into a thousand floating shards, suspended mid-air. The sky tore apart, revealing a void beyond the stars. Every cursed sigil on Zero's body exploded at once, releasing a scream so ancient and terrifying that even Muzan, wherever he was, felt it deep in his bones.
When the dust settled, Zero was gone—not even ashes remained.
All that was left was a massive crater, so deep it touched the earth's mantle, glowing faintly with residual heat.
Saitama landed gently next to Tanjiro, hands in his pockets.
"Welp. That's done."
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Aftermath
The Demon Slayers could barely process what had happened. Zenitsu was trembling, eyes wide. "H-he's a monster… a bald monster…"
"Strong," Inosuke whispered, for once without shouting. "I wanna fight him someday."
Tanjiro, though still shocked, smiled. "Thank you, Saitama-san. I don't know who you are or where you came from, but you saved us."
Saitama waved him off. "It's fine. But if you know where I can find some good ramen, that would be great."
The silence was broken by a soft giggle—from Nezuko, peeking out of her box. Even after all the chaos, somehow, Saitama's bald head was funny to her.
"Hey, what's so funny?" Saitama muttered.
The battle was over, but the legend of the Bald Hero in the Demon Slayer Corps was just beginning.
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End of Chapter 20