Chapter Text
Genos hadn't really known what to expect when he walked back into the apartment after being stuck on Kuseno’s table for days on end, but this was definitely not it. Saitama’s eyes lit up alpha white, only the second time Genos ever saw them do so, before he stalked over to the door. Saitama’s movements were almost predatory, and he took Genos’ chin in his hand and tilted his face to the side. Shoved his nose into Genos' neck, and breathed in deep. Genos shivered involuntarily, instincts that had been subdued for years now surging back to the surface.
It reminded him of the first time he’d encountered Saitama, and that puzzled look that had crossed his face. Saitama had scented Genos where he’d lain half broken in the street, huffing out searching breaths against Genos’ throat, as if looking for something he could not find. Eyes lit up, a growl lingering in his mouth, hands clutching at the metal of Genos’ wrist.
Then he’d pulled back, cocking his head to the side in a disturbingly canine way, brows furrowed at Genos in question. For the briefest of moments, Saitama seemed angry. Like someone had stolen from him, but he could not put his finger on exactly what had been taken. A sense of wrongness he felt but couldn’t place. A heaving sigh, a transitory snarl, and the light in Saitama’s eyes had faded away, never to be seen again. Until now, his lip curled back from his teeth as he nosed into Genos’ glands.
Glands he had not possessed before. Had not thought he needed, had not wanted to wear under the false skin of his throat, or tucked away into his thighs. People looked at omegas, or caught their scent, and their first thought was inevitably ‘weak’ .
Submissive.
Someone who needed protection. Someone who was not a threat, and Genos did not want those dismissive eyes falling on him before flitting away. Discounting his very existence before they even really looked at him. Genos wanted to be strong .
So when Kuseno had transformed him into a cyborg, cutting away his damaged flesh and replacing it with metal and wires and circuitry, Genos told the doctor to leave out the glands. Let him be a beta, no one would ever know, and he could live his life without the condescending stares of alphas on him. Kuseno had chided Genos, your brain is still an omega’s brain, I don’t know how this might affect you later , but Genos held firm.
The loss of his dynamic at such a young age had not affected him at all, really. It was harder to adjust to his new body than it was any loss of omegan instinct. By the time Genos could work the canons in his arms, or operate the analytics that flitted through the corners of his vision, he’d almost forgotten he was an omega at all. Until he met Saitama, that is.
Saitama, who was somehow both more and less alpha than any he had ever encountered. Saitama’s strength was unequaled, and he could beat any enemy without breaking a sweat. Destroy buildings without even trying, break open meteors with nothing but his fists. Monsters trembled in his wake, when there was anything left of them to do so, anyway. The other heroes who knew his true power did not even entertain the possibility that they might defeat him.
But he didn't challenge other alphas for dominance. There were no staring contests, no growling matches, no unspoken tension hovering in the air between Saitama and others of his dynamic. It was as though he did not posses the same instincts that sought to subdue and dominate. Saitama walked past omegas without so much as raising his eyes. Even those lost in the rush of their heats did not elicit a second glance from him. They looked at Saitama , to be sure, confused by such an overpowering scent coming from an alpha who appeared docile and unconcerned with them. It was bizarre, and unprecedented, and Genos did not quite know what to think of it. Still, even in its strangeness, it wasn't particularly troubling.
The longer he was around Saitama, though, the stranger Genos himself felt. His neck itched when he sat next to Saitama for too long, heat swelling up where his pulse would have throbbed, had he still possessed such a thing. Genos thighs wanted to squeeze together at the thought of Saitama. His hands on Genos’ armor. His thumbs in Genos’ mouth. His teeth on Genos’ skin. Fuck . He found himself tilting his head sometimes, exposing his throat to Saitama.
Submitting. Presenting .
Which was ridiculous. He was not an omega anymore, not really. Did not produce pheromones, could not go into heat. So why did Genos’ eyes sometimes hold Saitama’s before dropping away in submission? Why did his knees want to fall wide in answer to a question the hero had not even asked?
Begging with his body for something he physically could not have. Something Saitama did not want to give to anyone, let alone Genos.
Then Genos’ analytics began to glitch. At first it was only in the midst of battle as he strained his cybernetics to the breaking point. His throat would start itching, warmth spreading over Genos like a fog, and then everything went to shit. His targeting systems would shut off, leaving his heat canon firing blind. Vents not wanting open, failing to cool down his internal workings. He’d suffered a thermal shutdown once as they faced a horde of robots, leaving Saitama to finish them off by himself. Another time his neural networks went into overdrive, and even the wind blowing against Genos’ plating was enough to bring him to his knees. Genos tried to write it off as an issue with his brain implants. He needed new hardware, new cybernetics, and everything would be fine.
Except it was not, and even after Kuseno put new gear in him, circuitry so advanced it could run an army of cyborgs all on its own, Genos continued to have problems. Not just during firefights, but all the time. That telltale warmth swelled over Genos’ skin as he sat next to Saitama one evening, and Genos woke up to find Saitama crouched over him. Face a mask of concern, palms cupping Genos' cheeks as he called out his name.
Genos, Genos, Genos.
Laced with worry. Affectionate, in a way that Saitama rarely was with him. Genos had not glitched, or overheated, or gone into sensory overload.
He’d just shut down completely. No warnings, no error messages, no analytical screens flashing red. Genos turned off like a light switch, only to blink those gold black eyes open at Saitama a few minutes later in confusion.
It happened three more times before Saitama dragged him to Kuseno’s, and even then it had taken the threat of violence. Spoken in a voice that sounded bored, but brooked no argument.
‘I’ll tear your legs off and carry you there, Genos. You’re going to get yourself killed.’
Saitama was probably right, but that didn’t make Genos any more eager to go see the doctor. Because try as he might to come up with something else, there was only one reason Genos could think of for his systems to start going sideways all at once. His body might not age, but his mind was still human, and he was almost twenty years old.
Most omegas had gone into heat by then. Nineteen was pushing it, and Kuseno had warned Genos this could happen. That his brain might not understand the absence of his glands and organs, and try to throw him into his first cycle. According to Kuseno, there was only one way to fix it.
The doctor put Genos under, and he woke up with all sorts of things he’d rather have been without. Artificial glands in his throat oozing hormones out into his bloodstream. Soft flesh on the upper parts of his legs, more of the glands tucked away beneath it. From his hips to his thighs, on the outside at least, Genos looked totally human. The moment he first opened his eyes, looking up at Kuseno in the confusion of lingering anesthesia, Genos’ nose wrinkled in disgust.
He smelled of omega. Was omega, for all intents and purposes. Not that he could reproduce, and thank god for that, but this was bad enough. A scent that screamed weakness, more flesh to protect in battle.
A body that would betray him soon. Throw Genos into a heat, and he’d have to come crawling back to Kuseno’s to suffer through it, because even suppressants could not totally quell the ferocity of an omega’s first cycle. Kuseno told him he probably had a couple of weeks before things got too serious, his glands needing time to produce the hormones necessary for a heat. Genos had trudged home feeling defeated in a way he never had before. Beaten by his own body, never given a chance for victory. His very DNA conspiring against him, and Genos wanted to bash his face into a wall.
Then he’d come through the door of the apartment he shared with Saitama, and he was in Genos' face in an instant. Inhaling Genos’ scent, arm sliding around his back. One hand eased from his jaw and into his hair, fisting in the synthetic strands. Saitama was growling, and when he pulled back to look up at Genos his eyes were still alight. Wide, and full of wonder, looking at Genos like he had done something amazing.
“Genos.” Genos' jaw shivered as he tried to find words, head falling to the side, eyes dropping in submission.
As they always had for Saitama, and no one else on earth.
“S-Sensei?” Genos asked, and Saitama breathed in deep again, lips coming back from his teeth. Tongue tracing over them as though they itched to bite into something.
My throat. My thighs. Genos wished, anyway.
“You’re an omega .”
“Yes, sensei. Kuseno had to put my glands back. It seems that is why my cybernetics were glitching. I am sorry if this troubles you. I can leave, if I need to, until my hormone levels even out.” After his heat sometime, probably, but Genos kept his mouth shut. Saitama’s eyes flashed impossibly brighter, another growl easing out of his throat.
“You’re not going anywhere, Genos.”
Genos was stunned into silence, and after a few moments it seemed like Saitama came back to himself. Dropped his hand from Genos' waist, took a step away from him, shaking his head. Blinking his eyes, like he was trying to bring them back to normal, but they still shone bright and hot.
Throwing out light that danced over Genos, and he wanted to live in that possessive illumination for the rest of his life. Then Saitama stammered out an apology, hands fisted at his sides.
“Sorry. I… I’m sorry.” Saitama fled, taking off to the bathroom and slamming the door behind him.
Maybe he was sorry, but Genos was not. He wasn’t too sure exactly what had happened between them just then, but the omega inside him that he’d shoved aside for so long was alight with joy.
Savage, and victorious, and even if he had not triumphed over anything that did not seem to matter.
Soon. It would be soon.