In a distant future, around the year 3000, in a world unlike our own—where heroes aren't confined to comic books or movie screens but exist as part of daily life, just as police officers or firefighters do in our reality—a man from another world is reincarnated into one of this world's inhabitants…
A man who is a hero for fun.
Where am I? Why is it so dark? And… why can't I feel my body?
The man thought, surrounded by nothing but a suffocating blackness.
Ah… wait, I think I'm starting to feel something. My eyes… are they shut?
He slowly opened them.
As his vision adjusted, he realized he wasn't in his own room. For starters, the bed felt… off. Too firm. He blinked a few more times and focused.
Then it hit him—he wasn't on a bed at all. He was lying on the floor.
What is this? Why am I sleeping on a mattress on the floor? Though…
He pressed his hand against the surface beneath him, fingers tracing the texture. As his eyes scanned the unfamiliar room—bare walls, sliding door, a small low table shoved into the corner—an uneasy recognition stirred in his chest.
Wait a second… this isn't just any mattress. This is a futon! Like the ones they use in Japanese anime…
He sat up with a groggy grunt, feeling oddly light. He threw off the thin covers and stood slowly, the floor cool against his feet.
That's when something strange caught his attention.
His hands. They weren't his.
He had now thicker wrists, slightly larger palms and fingers covered in faint calluses, like they had known training and repetition.
These… aren't my hands.
Unease deepened as he stumbled toward the small bathroom attached to the room. The mirror above the sink was dusty, the light overhead flickering slightly. But when he looked into it, his heart stopped.
A blank face.
Empty, dead fish eyes.
And a perfectly smooth, bald head.
No… way…
He touched his cheek. The reflection mimicked him. He opened his mouth in shock. So did the mirror image.
He leaned in closer.
This is… Saitama. This is Saitama's face!
He took a step back, breath catching in his throat. He looked down again. The plain white T-shirt clung to a lean, muscular frame. Not overly bulky—just sculpted enough to seem effortless.
"This can't be real," he muttered, voice deeper than he remembered. "I… I'm Saitama?"
Panic and disbelief wrestled in his chest. The cramped apartment, the futon, the yellow curtains, even the battered electric kettle in the kitchenette—all of it was right. Every detail matched.
This isn't a dream. This isn't cosplay. This is real. I was reincarnated… as Saitama. And…
He began to look at various angles of the apartment
I don't see Genos here and the roof of Saitama is still intact, so it is very probably that I am at the start of the series, yess!! I will not start as a lame C-class hero!!
"I'm in the One Punch Man world," he whispered, almost laughing at how surreal it sounded. "I'm literally the most broken character in fiction, without counting gods and Goku, but I guess he count as a god now, so it's the same to me."
He collapsed back onto the futon, arms spread wide, staring blankly at the ceiling above him.
But… does that mean I'm actually strong now? Like, seriously strong? One-punch level strong?
There was only one way for him to know.
Still dazed, he got to his feet, moved to the sliding door, and stepped out onto the narrow balcony. Morning light bathed the city in a dull haze. The buildings were just as he remembered them—plain, distant and forgettable background buildings.
A gust of cold wind passed over his scalp. It felt weird.
So this is what being bald is like, huh…no wonder Saitama didn't like to be reminded of that.
He cracked his neck and then his knuckles while he exhaled long and slow.
"Alright… let's go find a monster or something," he muttered.
If this was really his new life—then it was time to see if the absurd power was real.
And if it was…
Then maybe the boredom will be real too.
Although…I wonder if I will keep the rizz the original Saitama had, I mean, he was a bald man with a hoodie that literally said boobs and still made one of the hottest chicks of anime want to have time with her.
However his thoughs were interrupted when he felt how a quake shaked his apartment, making everything tremble.
"Holy shit!! Is this what I think it is?!! Piccolo" He said just before running inside searching for Saitama's suit until he found it.
Once he changed, he went out to the balcony. The yellow pijamas with the red gloves and boots and a cape that looked more like a blanket than a cape. But it didn't matter to him, being on the body of a character you have only seen on TV or manga was a surreal experience to him.
That's part of the reason of why he hadn't thought of the implications of him reincarnating on this world infested with monsters and on a stolen body.
"Okay, now where are you?" He said as he observed the view from the city from his apartment, explosions flaring away distantly.
"Okay, now I gotta go down and run from here to there!!" He said, his hands trembling as he grabbed the balcony railing.
I am little high up here, isn't it? No, don't chicken out, you're Saitama, jumping from the balcony and land on the ground without any damage must be easy as counting to 3.
He thought unconsciously swallowing gulping as he saw down.
"Okay, I can do it, 1" He said as he grabbed the railing.
"2" He climbed up the railing.
"3!"
And with that shout, he pushed himself forward.
The air whipped past his face as he plummeted from the fifth floor, wind howling in his ears, cape fluttering wildly behind him like a cheap curtain caught in a storm. His heart seized for a moment—pure instinct screaming at him that this was certain death.
But then—
He landed.
Feet slammed into the pavement like it was nothing more than a soft mat.
There were no crack son the street. He felt no pain and hi didn't even stumble. Just a solid thud that echoed faintly in the empty street.
Holy shit… I just landed like a damn superhero…
He stood still for a moment, almost frozen. Then looked down at his legs. Still intact.
Then at his arms. No bruises, no soreness.
A grin slowly crept onto his face.
Okay… okay this is real. I'm actually built like him. I really am Saitama.
He looked around. The streets were mostly empty, but he could hear the distant sound of sirens, explosions, people screaming.
A trail of destruction loomed in the distance—shattered buildings, smoke rising in columns, and that distinct BOOM echoing across the horizon.
"That's gotta be Vaccine Man," he muttered. "Blue Piccolo-looking bastard, you're mine!"
And with that, he started to run.
The first few steps were normal—or so he thought. But within seconds, the scenery around him began to blur. Buildings zipped past him like background props in a cartoon. The wind pressure built around his ears as his boots pounded the ground in a steady rhythm that was faster than any car he had ever seen.
Wait—wait—am I even touching the ground anymore?!
It felt more like flying than running.
His eyes watered from the wind, and his cape nearly strangled him until he held it down. He glanced at a store window as he passed and caught a glimpse of himself reflected in the glass—a yellow blur with a red streak behind him.
This is INSANE!! I'm running faster than a sports car, and I'm not even breaking a sweat!
"Let's goooo!" he shouted, unable to stop the laughter bubbling up in his throat.
Each bound carried him meters forward. Cars honked as he flew past them, sometimes without even realizing he was using the sidewalk or not. The city whipped by in a montage of speeding lights and rising smoke until he reached the edge of A-City.
The destruction was unmistakable now.
A massive crater split a city block in two. One building lay in ruins, another halfway collapsed. And at the center of it all stood a towering purple-blue figure, veins bulging across his chest, antennae twisting as he roared at the sky.
Vaccine Man.
"Oh crap, he looks more terrifying in person…" he whispered, ducking behind a flipped truck.
But I'm Saitama. He didn't even flinch when he fought this guy. I should be fine… right?
He peeked over the edge.
Vaccine Man blasted a stream of energy into the air, the impact sending a ripple of shockwaves through the streets. Glass shattered for blocks, and a tremor ran through the ground beneath his boots.
Okay, no big deal… just a world-ending threat… nothing new. Just gotta walk up and punch him. That's what he did in the first chapter, right? One hit. Easy.
His legs shook despite his bravado. His brain still clung to the instincts of his past life—one where running into an anime villain would be a very stupid idea.
But this wasn't that life anymore.
This was his life now.
He took a deep breath. Then another.
"Okay… you've watched this moment like five times. You know how it ends. You've got this."
He stepped out from behind the truck, fists clenched, cape fluttering.
And then, he walked forward—each step taking him closer to the monster that would be his first real test as Saitama.
No fear. No hesitation. Just one punch… right?
The smoke thickened as he approached, the scent of burning metal and scorched concrete invading his nostrils. Fires flickered in craters where buildings once stood.
Screams echoed faintly in the distance—but one sound rose above the rest.
Crying.
A high-pitched, terrified sobbing that tugged at his instincts.
He turned toward the sound and spotted her—a little girl with a hoodie, crouched beneath a collapsed street sign, her cheeks dirty with ash and tears.
He remembered this. Episode one. A single scene, barely a minute long—but it had stuck with him for years. She had cried out for her parents right before the villain reached down and tried to—
"No."
He moved without thinking.
A shadow loomed behind her—massive, monstrous. A clawed hand descended like a guillotine from above, Vaccine Man's twisted face staring with hollow amusement.
Just as the hand was about to crush her—
He appeared.
In a flash, he slid in between, scooping her up into his arms. Vaccine Man's claw slammed into the pavement where she had been, shattering the ground with a thunderous boom. Dust and rock flew in all directions.
She gasped, clutching tightly to his chest as he shielded her with his body.
"It's okay. I've got you."
I did it… I actually saved her.
Vaccine Man snarled behind him, rising to his full, terrifying height—twice as tall as a man, veins glowing with bio-energy, antennae curling like snakes. He turned slowly, still holding the girl as he backed away.
He ducked behind a partially collapsed delivery truck and gently set the girl down, making sure she was hidden.
"Listen to me. Stay here. Don't move until it's quiet again, alright?"
The girl nodded shakily, wiping her tears.
"He's not gonna hurt you. I promise."
He stepped back into the open street.
Vaccine Man's eyes glowed with fury now, locking onto him.
"You're fast," the monster growled, his voice echoing on the desolated streets. "Who… are you?"
The words echoed in his head.
This is it. This is the moment. I remember this line. I REMEMBER THIS LINE.
He grinned, inhaled sharply, and clenched his fist as the cape behind him fluttered.
"I'm just a guy who's a hero for fun."
Silence.
Even Vaccine Man seemed momentarily thrown off by the flat, casual tone.
OH MY GOD THAT WAS SO COOL.
That was PERFECT. I nailed the delivery! The timing! The stance! That was anime as hell!
He bit the inside of his cheek to stop himself from smiling too hard.
I just said the most iconic line in the series… as the real Saitama…
But there was no time to savor it further. As Vaccine Man focused on him, his fase was contorted with rage.
"You are kidding, what kind of half-assed backstory is that? Mine's far superior. I was formed from the pollution…"
And this is where he starts to talk and talk about his origin and how humans bad because muh contamination.
He thought as he saw Vaccine Man talking.
"…You filthy humans are nothing but a disease-causing bacteria eating away at a precios life,"
"God, shut up."
Vaccine Man blinked.
"What?" he grunted, his tone momentarily more confused than enraged.
"Blah, blah, blah, I get it—humans bad because we throw waste on your ass. Cool. But you just killed, like, a thousand people in the last five minutes, so I really don't wanna hear you yapping about recycling ethics. I don't care. So please… just shut up."
The villain's face twisted again, this time with blind fury.
"You dare mock ME?! Witness my TRUE FORM, flesh sack!"
His body convulsed violently. Muscles bulged, skin tore, and bone cracked with wet snaps as Vaccine Man grew in size—twice, three times taller—his mouth stretching into a vertical maw filled with jagged fangs. A thick exoskeleton burst from his shoulders and chest, coated in fleshy purple growths.
Oh god, this is way nastier in real life than it looked in the anime…
The monster's roar echoed through the city, a guttural explosion of hate and power. Dust and debris flew in every direction.
But he didn't move, he just raised his fist.
Let's see how far the guts fly.
Vaccine Man lunged but befor he came too close, he punched.
The impact was instantaneous.
The moment his fist connected with the monster's abdomen, a sickening crunch echoed through the street—followed by an explosive burst of gore. Vaccine Man's entire torso detonated, as if a bomb had gone off inside him. Chunks of rib, shattered bone, and steaming entrails rocketed in all directions like confetti made of nightmares.
His spine whipped out of his body mid-air, flipping end over end before slamming into a nearby wall with a wet splat.
One of his eyeballs popped like a grape as it smacked against a fire hydrant. A piece of what might've been a lung landed on his boot with a soft flop.
And then… silence.
Just viscera, smoke, and half a torso twitching like a deflated balloon.
He lowered his fist slowly. Then stared at the carnage.
And gagged.
"Oh my—oh god—that's disgusting—" he choked, staggering back a step. "Ugh, what the hell—there's an intestine on my shoe!"
Oh my god, it smells… oh god it SMELLS—was that his liver or his pancreas?! Is that even a pancreas?!
He turned away, nearly vomiting, hand over his mouth.
How did Saitama do this every other week without throwing up?! What the hell, man!? This is SO much worse in real life!
He stumbled over to a broken mailbox and sat down on it, trying to wipe off a smear of blood from his glove.
Okay… okay… awesome punch. But holy crap, that was vile. They really don't show the details in the anime, huh?
He looked around at the carnage again, face pale.
I literally just turned a supervillain into soup. Hero for fun? More like trauma for life.
But still, under the horror… he grinned
After all, he had done it. He one-punched a kaiju-sized abomination and survived.
"Cool as hell… Disgusting as hell… but still cool. Now…how do I wash this shit away?"