Chapter 3: The Upper Moon’s Worst Mistake

The forest was eerily silent as Tanjiro, Saitama, and a still-unconscious Zenitsu approached the mission location. The air was thick with demonic energy, heavy and suffocating. Even Nezuko, peeking out from her box, seemed uneasy.

"This presence…" Tanjiro's grip tightened on his sword. "It's an Upper Moon for sure."

Saitama, on the other hand, was more focused on his growling stomach. "Hey, do they serve food after these missions? I skipped breakfast."

Before Tanjiro could answer, a low, chilling laugh echoed from the shadows. From the mist stepped Gyokko, Upper Moon 5, his grotesque fish-like face twisted into a sinister grin.

"A Demon Slayer and…what the hell is that?" Gyokko's eyes narrowed at Saitama's bright yellow suit and blank expression.

"Baldy," Saitama said, raising one hand lazily. "Just a hero for fun."

Gyokko's face twitched in confusion. "Whatever. You'll all die here."

Tentacles erupted from the ground, twisting toward the group. Tanjiro leapt into action, his sword flashing as he used Water Breathing: Fourth Form – Striking Tide to slice through the writhing limbs.

"Tanjiro! Be careful!" Nezuko's muffled voice called from her box.

But Saitama just stood there, watching the tentacles approach him. When one wrapped around his ankle, Saitama casually flicked his foot — and Gyokko's tentacle exploded into mist.

"Huh?" Gyokko blinked, stunned.

"You're pretty weak," Saitama said, bending down to pick up another pebble. "I thought Upper Moons were supposed to be strong."

Gyokko roared in fury, releasing a swarm of deadly fish demons from his pots. They swarmed toward Saitama, their jaws snapping —

SMACK.

Saitama clapped his hands together once, and the entire swarm evaporated. Tanjiro's jaw dropped. Nezuko gasped. Even Zenitsu stirred slightly in his sleep, sensing the absurd power.

"Y-You monster!" Gyokko shrieked, unleashing his final form, his body twisting into something even more hideous.

Saitama frowned slightly. "That's ugly."

Serious Series: Serious Slap.

With a casual backhand slap, Saitama sent Gyokko flying through five mountains, his body disintegrating before he even knew what hit him.

"Upper Moon 5… defeated in one hit," Tanjiro whispered, unable to process what just happened.

Saitama stretched, yawning. "That's it? I thought this would be more fun."

The crows circling above had already flown off to report back to the Demon Slayer Corps, and somewhere far away, Muzan felt a cold sweat run down his spine.

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End of Chapter 3