It is I, the narrator from the "Imagine the Dragon" chapter! Which means this episode doesn't need to make sense! Yay!

Well, of course that's not true, any story needs some kind of consistency.

Anyway, off we go!

Basically I'm... "borrowing" a certain bald hero from a totally different universe. He is so incredibly strong that he can defeat anyone with one punch. Pretty sure they call him "Baldman". So I'll call him that. Are you cool with it, Saitama?

He raised one thumb as to confirm. His face as meme-able as always.

So I'm borrowing Baldman and putting him in the Toaru universe. It's time to see how strong he really is. With the battle everyone was waiting for: Saitama vs Uiharu!

"Where am I? What is this place?" Asked the soft voice of the young girl, as she appeared in the void as soon as I mentioned her.

"So, you appear to be the strongest hero in your world!" Exclaimed Baldman, excited to finally get a good fight for once.

"What? I'm just a level 2!"

"I like your funny words, magic girl!"

Wait Baldman, you're going out of character. That's a line from Clone High.

The girl looked around, trying to keep her own skirt down as she floated in the whiteness of the place I put them in. "What was that voice?"

"Oh, just the narrator, he brought me from my universe to fight the strongest human in yours."

"I'm just good with computers though..."

Yeah, I'll admit it, I called her in just as a joke.

And with that, Uiharu woke up in her bedroom, confused by what appeared to be the craziest dream she ever had.

"So, when is my challenger coming? I'm yearning for a good fight!"

Fine. In that moment, Baldman found himself in front of this guy... what was his name again? Velocity-something? Vectordude? Not sure, but it's the white-haired #1 Esper. That guy. He was chilling in the aftermath of a fight he had with people trying to beat him. It was all exceptionally clean, though.

"So, what did this guy do? I need a reason to fight him you know?"

Yeah, he's bad. Like, he threatened someone. And I'm pretty sure he insulted a stranger at least once.

"Seriously? That's it?"

In that moment, the one and true Vectordude -yes, let's call him that- noticed Baldman.

"Who are you, assface?"

<<I see now.>> thought Baldman. <<This boy is clearly evil!>>
"I am One Punch Man. Wanna know why they call me that?"

Accelerator -no wait, I meant Vectordude- raised an eyebrow: "Because it takes one punch for you to lay on the ground crying?"

"What? No, that would be my enemies, you know. I thought it was kinda obvious."

"Ooh, looks like shitsuit is asking for a fight!"

Yes he is. This is the whole point of the chapter. Get it over with so I can get back home for dinner.

"Fine, mysterious background voice, I'll fight this guy here. I hope he can put up a decent fight, at least."

"Oh, I will. Try not to lose your kidneys when I punch you, boy." Was Baldman's answer, while he was warming up his shoulder.

Vectordude smiled: "You know, if this fanfiction was set after I met Touma, you mentioning that you wanna punch me with your right hand would definitely ring a bell and make me be more defensive. But hey, I guess I'm glad that did not happen yet in this setting."

A determined look appeared on Baldman's face: "Heh. Ready when you are."

"No, no, please, I want this to be fair. Show me what you got. You go first." Vectordude was behaving sarcastically kind, aware of his strength.

And then it all started. Saitama leaped at his opponent, his fist clenched as to deal the strongest punch he ever could. He packed a punch that would defeat even himself if he was fighting with his own copy. Well, not really, being invincible,  but you get the idea. Clearly this kid deserved it, after he called him "assface".

Accelerator waited, standing in his place. Ready with his ability.

And then it happened. One Punch Man's fist got within 0.1 mm of Accelerator's nose with a speed of 290,000 km/s (97% of the speed of light), implying a momentum of about 662,596,462 kg*m/s (that is, taking relativity into account). That's the moment when Accelerator's reflection ability activated.

You see, if you want to perfectly reflect a vector, you simply need to add a minus sign in front of it. Yes, that's it. That's how hard it is for Vectordude to use this power. No wonder he can do that subconsciously!

So, what happened here is that, as Saitama's momentum got a '-' in front of it, it got reversed. Meaning that if he was going forward at 97% the speed of light, he was now going backwards at 97% the speed of light.

A normal human would be crushed to death by this. But not Baldman. He was a durable guy! Problem is, he had to stop somewhere, right? He was flying away from his opponent at almost the speed of light. Luckily for him, a nice building was behind him and generously decided to absorb part of Saitama's current kinetic energy. Point is, his current kinetic energy was the equivalent of 5000 nuclear weapons, each equivalent to 1 megaton of TNT. Since Saitama doesn't know magic, he cannot just erase all that kinetic energy.

So, Baldman kept hitting on buildings and disintegrating them due to the immense amount of kinetic energy he was carrying, basically causing the equivalent of a small nuclear explosion for each obstacle he met.

Unluckily for him, Earth is not an infinite flat planet and definitely isn't able to attract effectively something almost as fast as light. So, as he was carelessly looking at all the walls he was hitting, without still receiving much damage (due to how durable he is), he got soon out of Earth's orbit.
Unluckily for him (again), he was not able to breathe in space. So he died.

Back on Earth, Accelerator looked at the incredible destruction in front of him. "Well, he did pack a punch, I see. Ironically physical strength won't defeat me as long as I have reflection. This fucking idiot doesn't even know physics huh? If he knew what vectors are he would've tried something different to take me down."

To be fair, he didn't know about your power at all.

"Oh well, F. Still just another guy who thinks muscles can beat brains. My mind can fuck up anything, I don't even need to move a finger."

Yeah, anything besides Imagine Breaker.

"What?"

Nothing... oh by the way I forgot to mention that the various "small nuclear explosions" caused by Baldman's body hitting on walls are enough to destroy a big chunk of the country. More than enough to blow all oxygen away for long enough to asphyxiate you.

(This was still before Accelerator thought about it fighting Touma, so he couldn't prepare for that.)

Suddenly, Accelerator dropped dead on the ground due to what I literally just said.

The end. It was fun, wasn't it?

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Author's note: I am totally fine with comments saying that with a different premise, the results would be different. But I will not accept comments disregarding physics in order to let one of them win. I also am open to reasonable discussions, but avoid butthurt comments. Butthurt comments would imply one didn't get the obviously ironic nature of this chapter. Take it lightly. I am not saying One Punch Man is a bad show.

I assumed Saitama to be physically indestructible, to avoid any complaint about it. I also made him punch harder than his regular punch: he is technically able to punch at 256266 km/s and at those speeds, adding 34000 km/s (roughly 13%) is HUGE.

I also assumed Accelerator used only his most basic power, not only to simplify my calculations, but also because ironically, more complex powers of his wouldn't be as effective against Saitama (assuming he is physically invincible).