CHAPTER 300: CHAPTER 1: THE WORLD OF THE BALD DEMON KING

"A large number of mosquitoes have appeared this year—it’s clearly a new species..."

"We interrupt this program with breaking news! A massive swarm of mosquitoes has been reported in Z-City. There are claims that livestock attacked by them are left as dried-up husks..."

Just as the emergency report aired on TV, warning sirens blared across the streets of Z-City.

"Wooo—woo—This is a level Demon disaster warning! All residents are urged to remain indoors! I repeat—this is an emergency evacuation order—"

Atop a building stood a blonde cyborg—Genos. He was staring coldly at the distant, swirling cloud of mosquitoes. A shriveled, desiccated bird lay at his feet.

"Target acquired," he murmured.

Not far from him, inside an apartment building—

A bald man was locked in battle with the greatest enemy of his life: a mosquito.

...

Meanwhile, on the rooftop of another skyscraper in Z-City—

The air began to ripple like the surface of water, warping space itself.

From within that distortion stepped out a tall, slender figure clad in a blue haori, his long ponytail swaying in the wind.

"This place is..."

Having crossed dimensions with the power of his system, Ron arrived here from the world of Demon Slayer. His eyes swept across the cityscape filled with towering buildings—structures he hadn’t seen in a long time. He was visibly taken aback.

"A modern metropolis?"

"Hm?"

Something caught Ron’s attention. He turned his head instinctively in one direction.

BOOM!

A deafening explosion erupted in the distance. A fiery blast shot up from the streets nearly a kilometer away.

Activating his Tenseigan, Ron saw it all clearly—the blond cyborg engaged in a fierce battle with a monstrous mosquito woman.

He froze for a moment, then his expression shifted.

"Wait a second... could this be..."

And then, he saw him.

A bald man chasing after a mosquito, wielding insect repellent spray with all the intensity of a seasoned warrior.

At that moment, Ron had no doubt left in his mind.

This was definitely the world of One Punch Man.

[Ding! Current dimension detected: One Punch Man World. Acquired 20 Sign-In Points. Option to return to the One Piece world is available. Scanning for sign-in location... Estimated scan time: 3 days.]

BZZZZZZZ—

High above the street, billions of mosquitoes converged into a black, twisted sphere, pulsating with ominous energy. Something powerful was being born inside it.

"So that’s a ’monster,’ huh?"

A glint of interest flashed through Ron’s bright blue eyes.

From what he knew, this world wasn’t just home to powerful heroes. It also spawned monsters capable of planetary-level destruction. And then, of course, there was him—the unbeatable bald-headed demon king.

Ron glanced toward Saitama and Genos, wondering to himself, With my current strength, where would I stand in this world?

Surely, there are worthy opponents to fight here...

Just the thought made his fingers twitch. He hadn’t had a real fight in the Demon Slayer world—no one strong enough to make him go all out. But here, his blood was stirring, every cell in his body aching for battle.

As he watched, the tides of combat turned.

Genos unleashed a torrent of fire, reducing billions of mosquitoes to ash.

But the evolved Mosquito Girl appeared behind him in a blink, her claws slicing across his abdomen, nearly cleaving his mechanical body in half.

Genos retaliated.

Mosquito Girl dodged nimbly, slashing again—this time ripping out one of his eyes.

Without hesitation, Ron teleported to a nearby rooftop using his Tenseigan, now observing the fight from up close. It was clear the battle was all but lost for Genos.

"No chance of victory left..."

"Only one option remains—self-destruct... Forgive me, Doctor..."

Genos, battered and broken, prepared to trigger his core’s self-detonation.

And just then—

Saitama, now entirely naked thanks to Genos’ earlier attack, appeared behind Mosquito Girl. Calmly, he brought down his hand.

SMACK!

Before she could even register what happened, Mosquito Girl exploded into a fine red mist.

"Finally got it."

Saitama grinned with satisfaction, arms akimbo.

"Mosquitoes are seriously the worst."

"...!!"

Genos, his body split in two, lay stunned on the pavement, speechless.

"Tsk, tsk..."

From the nearby rooftop, Ron rubbed his chin thoughtfully. His gaze fixed on Saitama. "To think that raw physical strength alone can reach such an absurd level... No doubt about it—he’s the real deal. The bald demon king himself..."

Mosquito Girl had always been weak—even after evolving, she didn’t amount to much. Ron could easily squash her with a single punch too, but she was in no way a benchmark for Saitama’s strength.

Right now, Ron’s vital energy value had already exceeded 5,000. A basic punch, relying on blood force alone, could shatter a mountain over a hundred meters tall.

But Saitama? He could obliterate meteors with his fists. He could level mountain ranges with nothing but the shockwaves of his punches.

If one were to quantify that kind of power into a "vital energy" stat, it would be downright terrifying.

At that moment, Saitama seemed to sense someone watching him. He turned toward Ron’s location.

But saw nothing. Just an empty rooftop.

Scratching his shiny scalp in confusion, Saitama muttered, "Huh... I could’ve sworn someone was watching me just now... Was it my imagination?"

"...Whatever."

He turned to leave.

"Wait!"

Genos called out, his voice strained from the wreckage of his body.

Saitama looked back, puzzled.

"Hmm? You still got something to say?"

"I am a robot who operates independently in pursuit of justice. My name is Genos. Please... tell me your name!"

"Ah? I’m Saitama."

"Saitama-sensei, please—take me as your disciple!!"

"...Huh?"

Just before Saitama could move again, Ron, having already foreseen the next second through Observation Haki, vanished from the scene without a sound.

...

Now dressed like an ancient warrior in a world of steel and glass, Ron strolled leisurely through the empty streets of Z-City.

Why had he left so suddenly?

He knew the answer all too well.

It had been so long since he’d faced an evenly matched opponent that his body was starving for a fight. If he had remained in Saitama’s presence any longer, he might’ve done something reckless—like challenge him then and there.

And that would have ended... predictably.

He would fight Saitama one day.

But not yet.

Before facing the bald demon king, he needed to reach the pinnacle of his strength.

And to do that—he needed battle.

Whether against heroes or monsters... it didn’t matter.

Fortunately, this world had no shortage of powerful foes.

As that thought took hold, Ron’s eyes began to shine. The blood in his veins surged with energy.

His bright blue gaze scanned the horizon, a smile curling on his lips.

"So then... where should I go first?"

—----------------------------

Note: Ron refers Saitama (Protagonist of One Punch Man) as Bald Demon King in this AU