The One Punch Man (a.k.a Saitama) in Demon Slayer

The moon hung high in the sky as the battle's aftermath settled over the battlefield. The once-proud Upper Moon Four, Juroku, had retreated in fear—a shocking event for the Demon Slayers.

Saitama yawned, scratching his head. "So… that's it? I thought he was supposed to be strong."

Rengoku laughed heartily. "AH HAHAHA! Saitama-dono, you truly are an incredible warrior! Your strength is beyond what I could have imagined!"

The other Hashira nodded in agreement, though Sanemi scoffed. "Tch. It's annoying how strong you are. But at least you're not an enemy."

Muichiro, standing silently, stared at Saitama with a thoughtful expression. "That punch… was it even your full strength?"

Saitama shrugged. "Not really. I was holding back a lot."

The Hashira exchanged glances. What if he had used his full strength? That thought alone sent a shiver down their spines.

---

Muzan's Fury

Meanwhile, deep within a hidden lair, Muzan Kibutsuji's rage was palpable.

Juroku knelt before him, his body trembling as he tried to explain himself. "L-Lord Muzan… that man—he isn't human. I don't know what he is, but he's stronger than any demon slayer I've ever faced."

Muzan's blood-red eyes glowed with fury. "Are you telling me that a mere human defeated you so easily?"

Juroku swallowed hard. "H-He sent me flying with just a flick… I couldn't even react…"

The other Upper Moons watched silently from the shadows, sensing Muzan's rage growing dangerously unstable.

"Pathetic," Muzan said coldly. His fingers twitched, and suddenly—

Juroku's body began to dissolve.

"AHHHHH!" Juroku screamed as his body melted into nothingness, his existence erased by Muzan's will.

The room fell silent.

Muzan turned to the remaining Upper Moons. "This… 'Saitama' must die. Find out what he is and destroy him."

Upper Moon One, Kokushibo, bowed his head. "As you command, Lord Muzan."

The hunt had begun.

---

Back at the Demon Slayer Headquarters

The Demon Slayers returned to the Ubuyashiki Estate, where the Master of the Demon Slayers, Kagaya Ubuyashiki, awaited them.

Kagaya smiled gently. "You have all done well. The fact that an Upper Moon was forced to retreat is a great achievement."

Tanjiro and the others knelt before him. "Master, Saitama-san's power… it's unlike anything we've ever seen."

Kagaya nodded. "Yes… he is a mystery. A man without limits, yet lacking purpose." He turned to Saitama. "Saitama-dono, do you wish to continue fighting alongside us?"

Saitama thought for a moment. He had no real reason to stay. But…

He glanced at Tanjiro, Zenitsu, and Inosuke. At Rengoku, Sanemi, and Muichiro.

These people weren't just strong—they were determined. They had something he didn't… a reason to fight.

Saitama sighed. "Eh, sure. Not like I have anything better to do."

Kagaya chuckled. "Then I welcome you, Saitama-dono, as an ally of the Demon Slayer Corps."

---

Training for the Future

With the battle over, a new challenge began—training.

Though Saitama didn't need training, he still joined in out of boredom. Watching him train with the Hashira, however, was a sight to behold.

During a sparring match:

Sanemi tried to land a hit on Saitama with his wind-enhanced sword strikes—but missed every time.

Muichiro attempted to predict Saitama's movements using Mist Breathing—but Saitama was just standing still, and he still couldn't touch him.

Rengoku challenged Saitama to an endurance test… only to collapse from exhaustion while Saitama remained completely unfazed.

Meanwhile, Tanjiro and the others trained harder than ever. They knew that if they wanted to truly stand alongside Saitama, they needed to grow stronger.

Tanjiro clenched his fists. "We can't rely on Saitama-san forever. We need to be strong enough to defeat Muzan on our own!"

Zenitsu, surprisingly serious for once, nodded. "Yeah… even if he's insanely strong, we have our own battles to fight."

Inosuke cracked his knuckles. "Hah! I'll be stronger than even the Bald Cape one day!"

Saitama, hearing that, raised an eyebrow. "Good luck with that."

---

The Next Threat Approaches

As training continued, the Demon Slayers remained unaware that Muzan had already begun planning his next move.

A new demon was lurking in the shadows… one unlike any they had ever faced before.

A demon designed specifically to counter Saitama.

The stage was set.

And soon… the war would truly begin.

---

End of Chapter 80