Notes: Canon Universe, established relationship.

It started soon after Dr. Kuseno found what was left of him in the dilapidated wreck of his hometown.

Even years later, Genos still remembered how that conversation went, the memory of the doctor's weary sigh clear as day in his mind as the man suddenly stopped what he was doing to look at him with a heavy gaze.

"You need to relax, my boy."

"What," he answered flatly, his voice a mixture of offence and disbelief.

Relax? How could that old man ask him to relax when they still didn't have any news on the whereabouts of the mad cyborg? When he wasn't ready to even face him, weak and useless as he was, let alone fight him? The doctor had been looking for that monster for years, surely he understood how important his revenge was?

With all the finesse of an angry teenage boy, Genos told him exactly where he could shove his advice.

It was a testimony of Dr. Kuseno's patience – or maybe the fact that he was by now far too used to those kind of comments – that he simply laughed at him.

Silence filled the underground laboratory once again, occasionally broken by the clatter of fingers on a keyboard or random high pitched chirps coming from the multiple computers and other pieces of equipment around them. The new familiarity of the scene was enough to lull the teenager into a false sense of security, thinking to himself that the doctor had decided to drop his crazy idea.

No such luck.

"Just," the old man started again an hour later, seemingly distracted by the mess of wires he was patiently untangling from his left shoulder and connecting to his new metallic arm. "Look up some techniques on the Internet, perhaps? Isn't that what young people such as yourself like to do nowadays?"

Genos wasn't sure there was a way to say that all the parts of him that gave a shit about what 'young people' did died along the rest of his family without sounding over dramatic.

He told so him anyway.

Unsurprisingly, the doctor laughed again.

Eventually, begrudgingly, when the sleepless nights, the pain and the stress just became too much, the teenager ended up doing just that. At this point, he would have given anything for a distraction and this seemed as good as any. Still, it probably took him way too long to realize that trying to fall asleep to another hours long playlist of mind numbingly boring music just wasn't going to do him any good.

Genos was just about to give up when, after a week of fruitless research time spent between painful upgrades followed by the even more taxing rehabilitation, another video caught his eyes.

The term itself – ASMR? - was unfamiliar to him; he'd never been a fan of technology, despite what he was slowly turning into, and even before, he'd never really spent a lot of time on his old school's library computer, even for research purpose. And this was not something he had ever encounter in any of the books he had read in the past. In the end, curiosity and boredom won as he clicked on the thumbnail, expecting another useless piece of junk video that would do nothing more than make him loose another twenty minutes of his life.

What he got instead was the weird close up of a woman talking in soft tones, explaining exactly what that ASMR thing was and what it stood for while something was suddenly happening in his head.

The feeling was... strange. Good, but strange, like little starbursts bubbling in his brain and down his spine, making him want to just stay there and listen until he fell asleep, away from the world. Away from everything.

He was transfixed.

It wasn't much. Not during the first couple of months when his body slowly but surely started to feel less and less human and more like a machine, metal, silicone and wires creeping higher and higher as the blood, the bones and the human flesh was eaten away in his need for revenge. Not when, later, the last piece left of his humanity was a brain floating in his cyborg body, his senses still so dull at the time that most days he simply couldn't even feel anything.

No, it wasn't much, but it was enough to calm part of the anxiety and the boiling anger for a time, to make some of the pain more bearable, to starve off the worst of the sensory deprivation that came right after the end of the transition.

It wasn't really much of an issue, at first.

Even after Genos became a fully fledged cyborg, a lone wanderer looking for the monster who destroyed not only his family and his village, but also every single bit of the normalcy of his old life, those feelings weren't something he had the opportunity to experience very often. He had other things to do, always moving and fighting and searching. Clearly, there was no time to allot to something so frivolous now that he was out of the lab.

And then he met Saitama.

Saitama with his incommensurable strength, his unparalleled sense of justice and his voice.

Usually, it wasn't so bad. Saitama wasn't much of a talker and Genos could fill the silence for the both of them when prompted. And even then, his sensei's voice didn't usually have that strange soothing quality he found in some of the people he'd managed to discover on the Internet over the years.

Nothing to worry about there, really.

But then, when the other hero got especially serious before a promising – but always so disappointing – fight, or when there were so many stores to hit for sales and so little time to do so, his tone would shift, a bit lower, a little slower. And later, when the line between teacher and disciple started to blur and they became more, the late night conversations accompanied by hushed voices became the norm instead of the exception.

That's when the tingles in his head would start.

Which was another problem in itself. How do you even tell the one most important person of your life that sometimes, your brain felt fuzzy when the we're talking to you without sounding like a creep?

It's simple. You don't.

"Oi, Genos."

Blinking, the teenager lifted his head, eyes tearing away from the screen to look at his teacher. The man, despite his usually inexpressive face, seemed almost uncomfortable for some reason. Sensing he should probably pay attention, Genos paused the video he'd been watching for the last 15 minutes or so – another one of those, it couldn't do any harm after the hectic week they just had -, locating his notebook in case he ended up needing it.

You could never know when someone as wise as his sensei was about to drop another one of his invaluable pearls of wisdom.

"Yes, sensei?"

"You're not..." Discarding his manga on the floor next to him, Saitama turned to face him fully, visibly bracing himself before opening his mouth again. "Dude, you're not watching porn, are you?"

The subsequent amount of steam that shot out of his vents would probably have been enough to fog out the entire living room of their apartment had the balcony door not been cracked open. If it was at all possible for people to die of mortification, the cyborg was sure that now would have been the perfect occasion.

"Wha- sensei!" he spluttered, closing his computer by reflex with almost enough strength to break the screen even though he didn't have anything to be ashamed of, thank you very much. "How- why?"

Raising his hands in defence, Saitama shrugged helplessly. "It's just- you've been staring at your screen for a while now, and you're not doing anything, dude. And your, uh," Gesturing at his own face, he hesitated a moment before adding, "Your expression is just... I don't know, man. Forget I asked."

Genos could have sworn his face was burning if not for the fact that he knew he had lost the ability to do so for a long time, now. Still, that didn't stop him from lowering his gaze to the table, trying to not only tone down his embarrassment, but also find something to say that wouldn't make Saitama judge him.

Not that his sensei would, of course. He was, after all, too much of an amazing man to ever do something like that. Only, it always seemed so hard for the ones who didn't experience those kind of sensations to actually understand.

That simple fact was almost enough to keep him from saying anything despite the uncomfortable tension he could feel growing steadily around them. Or at least, until his desperate need to give an explanation won against his desire to simply keep that part of him silent, boiling over in, he had to admit, perhaps not the most dignified way possible.

"Sensei! I want to explain!"

As soon as the words left his mouth in what was almost a yell, the cyborg couldn't help but cringe inwardly. Clearly, with all the time he had taken to compose himself, his window of opportunity to avoid making this even more awkward than it was had closed already, right? His sensei obviously thought so, if one was to believe the slightly taken aback look on his face.

"It's, uh, it's okay dude. You do whatever you want, you don't have to-"

"Please! Allow me, Saitama-sensei."

Throwing him an almost suspicious look over the top of his manga, Saitama eventually gestured him to go on.

"So, let me get this straight."

Sitting in perfect seiza at the other side of the table, Genos waited in silence, not wanting to put him off with another long winded explanation. Despite Saitama's patience, he honestly wasn't sure how much of what he just said the other hero actually understood.

"There's this AR-something in your head that makes it sometimes feel all nice and tingly."

"Yes, sensei."

"And it happens when people are, like, whispering and stuff?"

"As always, sensei knows how to find the right words to perfectly sum things up."

"And you definitely weren't looking up dirty stuff in the middle of our living room?"

"Saitama-sensei! You know I would never-"

"I know, I know," Saitama said while flapping a dismissive hand in his direction. "I was just kidding, sheesh. But, uh, yeah. That's... cool, I guess."

Right away, all the tension that started building up in his synthetic body was released, a slight smile finding it's way on his face. Really, Genos should have known not to worry; not when he had a sensei as perfect as Saitama. His relief was almost enough to miss the slightly considering look the other hero sent his way before said man started reading his manga again.

Almost, but not quite.

And that was it, for the most part. Things continued as they did before, and the topic wasn't brought up again.

Or at least, not until the latest Hero Association meeting he was strongly suggested to attend to.

Alone.

As if Saitama wasn't the most capable hero of them all. As usual, most of the S-Class didn't even bother showing up, and the few ones who did, him included, probably all wished they hadn't. A colossal waste of time, if one where to ask him, especially since it was about something no one gave a damn. Which, all things considered, hasn't been that bad until another useless argument broke out between some of the heroes, making the remaining hour even more unbearable than it was to begin with. Honestly, some of them could be so fucking frustrating.

Especially that annoying little green goblin. The way she just kept disrespecting Saitama was just unacceptable.

"Bad day?" The man asked when he finally came back fuming, listening patiently – or at least doing a great job of pretending to – until Genos ran himself dry after almost half an hour of uninterrupted ranting.

After several minutes, probably sensing his leftover agitation – as if the way he kept looking at the table like he was seriously considering burning it to the ground wasn't enough of a clue -, Saitama eventually reached over to where he was silently seething. The gentle tugging on his arm made the cyborg finally relent, letting himself be moved enough to put his head on the man's shoulder.

"So," Saitama said, clearing his throat, face almost pinched in discomfort. A strange occurrence, really, considering they'd passed the cap of casual touches months ago. "Did I tell you about that great deal I found in D-City earlier today?"

Without waiting for an answer, he then started getting into the details. How much he bought, how good the hot pot they were going to make tonight with all that discounted food was going to be, and had he mentioned the fresh cabbage he had found for only a third of the regular price?

Lost in the midst of his sensei's story, the first tingle at the back of his titanium skull almost caught him by surprise. Yes, Saitama's voice could hit just the right kind of triggers to make him want to go lax and listen to him for hours, but it was usually always during very specific kind of circumstances and this just wasn't one of those.

Genos was seconds away from asking him what he was doing when he noticed the faint pink tinge of Saitama ears, the hero's eyes staring resolutely at the wall in front of him.

Oh.

All of the sudden, his mind went back to that moment, weeks ago, and that look his sensei had given him. Genos had assumed Saitama had forgotten all about it, or just didn't care much about the whole conversation after his first moment of fleeting interest had passed. It seemed that, once again, the cyborg had underestimated the man.

That, or Saitama cared about him more then he'd thought at first.

Closing his eyes, core surging with unexplained warmth, Genos pretended not to notice, silently urging him to continue. His mind started relaxing more and more as the nervousness slowly bled out of Saitama's voice, his body following suit as the tingles occasionally caused him to almost shiver when they ran down his mechanical spine.

Then a short pause, before a low "That's alright?" reached his ears. The man must have taken his vague noise of affirmation as a yes, because he only stopped for a couple of seconds before he kept going, calmly explaining exactly how much he managed to save with the combined coupons and sales of today's grocery shopping.

When he normally would be paying a lot more attention to what the hero was saying – maybe hiding somewhere in there was the secret of his sensei's strength -, Genos stayed still, letting Saitama's voice wash over him, luring him into this in-between place right at the edge of sleep and wakefulness.

At this moment, despite everything, all was right in the world.

And really, the fingers that kept slowly carding through his hair were just an added bonus.

Melodies stuck inside your head
A song in every breath

A/N: I couldn't get the idea out of my head so I decided to give it a shot. I personally do not experience ASMR, though, so everything is to be taken with a grain of salt.

English is not my first language so don't hesitate to point out all my shitty mistakes!