This was a writing prompt from fellow author Ondori-Naramaki, a good friend who has quite the imagination.
Hope I hit all the marks! XD

With a clap of his hands, the towering pillars of acrid grey smoke dissipated in a forceful yet controlled wave. Billowing out of sight and to the edges of town in barely over a blink, leaving behind instead a clear view of decimated buildings and torn up roads stretching just as far. Most of which had been caused either directly or indirectly by the menace the tv reporters had taken to calling 'The Teleporter'.
An insect like being whose sole purpose seemed to be appearing in the exact place at the exact time to cause maximum mayhem. And then disappearing without a scratch.

Every C, B, and A class hero who'd faced off —or attempted to face off— against the merciless marauder had so far either been completely ineffective, or been caught up in the wake of this newest monster's wrathful wave of wreckage.
It had made Saitama's morning more of a countdown than a day off as he'd watched the villain's simultaneous progress across the countryside and up the hero board, knowing that he'd need to step in if it went any farther than-

And then Genos had arrived, telling him that they needed to mobilize and help with this newest unstoppable threat.

Saitama'd smirked, entertained as always by his student's enthusiasm, and in a flash he was dressed for success and following Genos out the door toward yet another effortless victory.

But all of that had come to a sudden, sickening, screeching stop. Right when it'd looked like the win was just one swing away.

And Saitama found himself standing there, rooted to the spot in the center of a newly smoke free city, searching the median and far off rubble for the silver glint of metal, the gleam of a bent cog, anything to confirm what he'd just done.
What that monster had made him do.

He'd pulled his punch, he just knew he had... right? It all happened so fast though, and he'd been primed and ready to squash that destructive disappearing act.

Saitama was fast, he knew that, but this villain wasn't just 'fast': they were instantaneous. And that was the problem, because speed he could handle, but he wasn't a psychic. He couldn't guess where that delinquent was going to pop up next.
He could get there within an instant of spotting them, but that insectizoid seemed to also have some sort of super heightened reaction time, 'cause Saitama hadn't been able to touch them.

Not until that human sized fly had finally slipped up and stood still for longer than it took to twitch its antennae and disappear for the umpteenth time.

He should have seen that for the trap it was. But he'd never expected anything like what happened next.

But it'd happened all the same.

He'd definitely pulled that punch. He'd at least pulled it to the side. Away from the center mass of the one that The Teleporter had summoned to take their place. The one who'd been scouring the wrecked cars and collapsing buildings for people in need of rescue. The one who Saitama'd instructed to stay on the fringes and help the citizens while he took care of the one causing all of that chaos.

He'd redirected it as hard as he could on a fraction of a moment's notice. He had to have. Otherwise...

He knew a cyborg body was sturdy; could stand up to a lot, but Saitama had yet to come across anything that could stand up to the raw power of even his softest punch. Let alone-

"M-Master?"

No, Saitama thought with a flinch. That wasn't the voice of his student. Right next to his head. Couldn't be. Genos didn't address him in that tone. Never had and never would. Because that tremble, that warble, wasn't one of exhaustion or confusion: it was one of fear. And Genos, his student, his friend, didn't- would never have a reason to fear him.
Because Saitama would never do a thing to hurt...

That was when he realized where Genos was. Why his student's voice had come from so close. And it was for the same reason that his bicep felt like it was wrapped in metal.

Because, to his mounting horror, his arm was stuck right through Genos' chest, just off to one side of center.

"Master?" The cyborg asked again, this time while his wide eyes searched his teacher's, right before they trailed down and grew ever wider at the sight of... his master's arm disappearing right into the place where a metal shoulder met a metal collar bone.
And then the guy was staring- gaping at him like he didn't believe what he was seeing.
Just like Saitama didn't.

"Genos, I-I don't- I didn't-" Saitama stuttered as he made to pull his arm out of the terrible, terrible-

"No, don't-"

But by the time he heard the protest, Saitama'd already yanked his appendage free.

Genos' eyes went impossibly wider at the sudden move and before either of them could so much as blink, a great fork of lightning arced through the newly empty hole in his chest and every one of his joints locked up, forcing his body perfectly straight with an audible snap.

Saitama jolted forward and caught the cyborg as his heavy, rigid frame threatened to overbalance, glad even through his panic that his hero outfit included a pair of insulating rubber gloves.
"Genos? Genos?!" He asked, heart kicking into high gear when the stiff friend in his hands did nothing more than twitch against the menacing crackles of electricity the gaping space in his chest was still pulsing with.

Unsure what else he could do, Saitama braced himself and did his best to keep a clear head. Trying and almost succeeding to take a deep breath in and out as he clutched his seizing student close. Wishing he could unsee- undo those horrific last few moments of both their lives.
Wishing he could rewind time. Back to that morning. Back to when the dutiful cyborg had told him they were needed in the city.

If he could do it over, he'd tell Genos to leave it to someone else. Maybe then his best friend wouldn't be frying in his hands. Leaking both hot and cold oil out onto his gloves and down his sleeves at a disturbing, alarming rate.

Eventually, when the light show finally began to peter out, the yellow eyes that hadn't done anything but stare a glazed and unwavering forward turned to those of their master, and though he found no look of recognition in them, Saitama held the contact like it was his duty. Until the sputtering electricity gave one more worrying crackle and stopped completely.
But by then, the soft glow of awareness had faded from a pair of eyes already fast on their way to shut.

Then, suddenly as he'd frozen up, the cyborg went boneless in Saitama's arms, nearly slipping out of his grip as the hero's frazzled mind stumbled to compensate.

"Genos?" Saitama asked, unable to stop himself though he knew full well he wouldn't be getting an answer. Rooted were he stood as he waited for it anyway.

At the faint hum of something from deep inside his friend's chest though, the caped crusader gave his head a firm shake and pulled himself to his full height, realizing at long last that there was something he could do for his damaged student.

With a quick check that he wasn't about to damage Genos further, Saitama rearranged the limp form in his arms for travel, coiled all of his running muscles simultaneously, and took off at top speed for the only place that could possibly help. Not bothering with a knock as he swept both himself and his ailing friend through several doors which eventually led him to a workshop where their sudden appearance startled the no longer lone scientist within.

"What in-"

"Genos needs help," Saitama blurted, aware that often enough, in situations like those, every second counted.

Maybe catching sight of the oil which Saitama could feel spreading to coat most of his front, the doc with the worried face motioned to a slab like table and hurried off to flip a series of switches, powering on a cluster of weird machinery that hung from the ceiling above it.

Without a word, Saitama deposited his perforated package on the center of the workspace and backed to a nearby bench where he sat facing the gruesome scene. Soon hanging his head in his hands when watching his student being worked on by a frantic mechanic made his stomach churn.

Closing his eyes when the bright heat of blow torches and the aggressive, flying sparks of metal cutting saws threatened to blind.

Leveling out his breathing when the high pitched whine of power drills threatened to destroy his forced calm.

Saitama wasn't sure when the jumbles of hectic activity and harsh noise stopped, but at some point it did. Presumably not long after that, the doctor addressed him in an exhausted, though decidedly not defeated, tone.

"He's back online. He should wake up any minute now."

"Thanks, Doc," Saitama said as he looked up in time to watch the tail of a white lab coat flap out the workshop door. Then, with a sigh, he looked over at the cyborg on the bio-machinist's table.

At least he'd managed to miss Genos' vital workings, he reminded himself as he rehung his head in his hands. Because judging by how quick the doc had been working, it had been just good enough a miss to buy him time to get his friend into the shop.

He just hoped Genos didn't look at him different after this. Hoped that they could still be master and pupil and go grocery shopping on sale days together and spend down time playing video games and eating ramen together.

He hoped the guy who'd refreshed his purpose in life and kicked his hero career up to the professional level- the guy who made him get out there and fight villains and enjoy it- the guy who'd made him laugh and feel again didn't... stop.

Saitama didn't want to go back to how things had been before he'd met and been followed home by the cyborg. Didn't want to be lonely and bored and just 'going through the motions' ever again.
Having a friend felt too good.

Having Genos as a friend made him happy. And he didn't want to say goodbye to that feeling. Almost as bad as he didn't want to say goodbye to the first real friend he'd made in-

"Master?"

And when Saitama raised his head from its slump, he realized his eyes had gone moist. But at the picture before him, of his pupil awake and staring at him the way he always did, he couldn't bring himself to care.
Genos was alive.

"Master, has The Teleporter been defeated?" Asked his pupil, words infused with enough confidence that it made Saitama just that bit more disappointed in himself.

"No," he managed around a growing lump in his throat.

"Don't worry, Master. We'll get them next time," Genos assured. At which, Saitama had to bite down against the sudden and overwhelming urge to outright forbid his student ever going anywhere near that monster again.

Instead, he took a moment to calm his near panic and looked Genos in the eye.
"So, you remember the fight?" He asked, shoulders tensing without his permission.

"My memory files are intact, yes," Genos said as he sat up on the table.

"And you remember how you got here?" Saitama asked, not sure which answer he was hoping for.

"I have vestibular and sense memories of it. Judging by my internal logs, the journey took no more than thirty seconds," Genos said with an 'if I'm not mistaken' look on his face.

"Then I guess you remember what happened between, huh?" The hero on the bench asked, eyes averting at the thought.

"...Yes. I do," Genos informed with an uncharacteristic pause.

"...And?"

"And it was painful."

"Yeah?" Saitama asked, looking up when he realized how soft Genos' voice had gone.
How soft both of their voices had gone.

"Very much so," Genos confirmed with a stiff nod. "Especially the short," he added, bringing a hand up to touch the place the doc had gone white upon seeing open and exposed as it had been when Saitama had swept them in.

"I pulled my punch. I swear I did," Saitama promised, eyes even moister than they had been a minute before.

"I know you did, Master."

To that, Saitama blinked as he realized that his student's words, as full of conviction as they'd come, had shaken a tear from him.

"I was studying your fight; working on an algorithm that would help us in tracking and eventually in predicting The Teleporter's teleportation patterns. Then, as I cleared a young couple from their burning car, you had your first clear shot and I took a moment to calculate your trajectory. It was perfect. But then, something grabbed me from behind and before I could break away, I was in the path of that perfect trajectory. And then, suddenly, it wasn't perfect anymore."

The earnest look in his student's eyes made Saitama forget anything he might have been about to say on the matter. Instead he found himself sitting there, returning the stare as he searched Genos for any stray sign of resentment or blame or fear or any clue at all as to how the day and all of its tragedy was effecting him.

"There is no need to worry, Master, I am back to one hundred percent. Thanks to both you and Dr. Kuseno," said the cyborg who had allowed himself to be studied without interruption far longer than most might.

"It's more... I know you're body's fixed, but-" Saitama cut himself off, gritting his teeth as he pushed himself to a sudden stand. This time searching his pupil for a reaction.
"How can you stand to be near me? After what I did to you?"

"What?" The surprised blink proving that the cyborg was in the very least taken aback, Saitama knew the line of questioning couldn't be far off the mark. So he pressed on, even if he didn't actually want to hear his suspicions confirmed.

"We were coordinating; working that disaster together. We were supposed to save the citizens, defeat the villain, and have some fun doing it. We were supposed to have each other's backs but instead... I put a hole through yours. Can you honestly look at me and say we're okay?"

At that, Genos, movements smooth and efficient as ever, positioned himself at the edge of the table and stood. Only then, with eyes that hadn't wavered from his teacher's, did he speak.
"We're okay."

"Really?" The hero in the oil smeared costume asked. Desperate to accept the answer, but not ready to believe it.

"Master," Genos started, before he reached out and took Saitama's wrist in his hand and lifted until it was virtually shoulder level.
"I trust you with my life."
Then he pushed the loosely folded fist shape against his chest. Exactly where that same fist had hit him earlier that day.

"Why?" The only word Saitama could fight past the fall of two more unexpected tears.

"I'm still here, aren't I?"

A raw, surprised laugh busted out from somewhere deep in Saitama's chest at the straightforward statement.
In response, Genos pressed the half fist a tad flusher against his chest and then gave his master the whole arm back. Expression hopeful.

"So, what do we do now?" Saitama asked as he forgave himself for the outburst.

"I suggest we track down that villain and, with my extrapolation algorithm and your fighting prowess, take them out together," Genos said with a self-assure nod. Going on when Saitama didn't move to agree. "Then, we could go for ramen. Your treat."

Well that tore it, Saitama thought with a growing, ever so slightly watery smile, Genos didn't hold the near life ending mistake against him and the two of them were still exactly as they had been: friends. Teacher and student. Master and pupil. Heroes for fun. And for justice. Together.

But, Saitama realized as his student returned the smile, that didn't change the fact that if Genos had been even an inch farther to the wrong side at the moment of impact... he'd be a smear of atoms painting the far off buildings an even darker shade of grey.

Saitama was never going to let that happen.

Genos had come back from similar injuries in the past, but that didn't change the fact that this particular injury had been exactly the kind of thing that got too many innocent people killed: Collateral damage. And Saitama didn't have it in him to watch innocent people, let alone a seeker of justice, get hurt because he'd grown complacent. Was too cocky to train like his life depended on it.
Like his best friend's life depended on it.

Like Genos' life depended on it.

So, as the two heroes turned to walk out the workshop and back out into a world that definitely needed they're help, Saitama glanced over at his student and made himself a promise:
That his training would never be over until he got so fast, so keen of sight, so fine a grasp and control of his cosmic level strength that he'd never hurt his friend again.

And this training was going to start with their tag-team takedown of the Teleporting Terror who'd come far too close to tearing the two apart.
For good.

XxxxxxxxXxxxxxxXxxxxxxXxxxxxxXxxxxxx

That evening, splattered in bug like guts and matching the descriptions of the heroes who'd finally managed the impossible feat of defeating the country's latest monstrous scourge, the victorious duo were treated to free ramen. And then a complimentary second round. And dessert. As a thank you for saving the city.

As Saitama gummed down the last of his mochi, glancing across at the partner in crime stopping he'd nearly- who'd nearly died earlier that day, he made a mental note to pick up the tab the next time they went out to eat.

After all, he thought with a held in laugh as he watched Genos struggle to cut his own sticky treat into neat, bite sized pieces, he still owed his friend a meal.
Or maybe several.

Naw, Saitama decided as his pupil finally followed his example and gave the table manners up as a lost cause, Genos was never picking up the tab again. Not so long as the two of them stayed friends who fought monsters and faced impossible odds side by side.

Saitama smirked as he realized he might just have promised himself to a lifelong commitment of beating Genos to the check. But as his student sent him a tiny, contented, mochi filled grin, he also realized he'd never want it any other way.

Wow. That turned out a little longer than expected. But I'm happy with myself so please feel free to be happy along with me! Lemme know what ya thunk and have a wonderful time with the new season of One-Punch Man!