Everyone assumed Steve was still an omega, since that's what he'd been before the serum - it had been deemed more appropriate to use the serum on an omega to get the best of both worlds: omega intuition and care with the alpha-esque qualities that the vita-rays provided. But it had turned him into an alpha anyway. It was hushed up and kept a secret. He was quiet, artistic, a soft heart still, but his size and strength and excellent leadership skills were all alpha. He'd fake it when it suited him, but now he was an alpha through and through.
Everyone had also assumed that the son of the great Howard Stark, future leader of Stark Industries was an alpha, and Tony Stark had happily let everyone keep thinking that. He might as well have been an alpha with the way he carried himself. The suit more than made up for any physical disparities there might have been, and his larger than life personality meant that no one even for a moment thought he was an omega. It was easy enough to fake alpha-dom with enough cash and experimental pheromone suppressants. His conquests usually assumed Tony just didn't want to knot for fear of paternity suits. He took care of his own heats, rare anyway since he'd been using all manner of suppressants since he came of age.
Steve had no reason to assume otherwise, and Tony took Steve for an omega along with everyone else. He figured maybe that was why his dad had liked him so damn much. There'd always been rumours about them, always were when alphas worked so closely with unbonded omegas, and Captain America was the most prized omega of all.
But then they met, and shook hands, and they knew.
Steve breathed in hard, trying to pick up a trace of the alpha scent that Tony should be throwing off if they really had just bonded, but there was nothing. Although now he was paying attention, the alpha smell from him was perhaps a little too intense. What he'd initially read as potent alpha now seemed a little too strong. A cover up.
Tony just stared at him open mouthed before picking a fight.
"So that was a bond, huh?" Tony said nonchalantly a few days later, once New York was half rubble. "I thought it'd feel a little more, I don't know, emotional."
They were driving back from SHIELD HQ in the back of Tony's limo after yet another debrief/chewing out/congratulating session. Steve swallowed. He'd been half-looking forward to, half-avoiding this, and it was just like Tony to come right out with it, address the elephant in the... car in an entirely un-omega-like way. The little he'd managed to learn about Tony had confirmed his suspicions that he at least acted like a cocky alpha, a know it all, arrogant jerk.
"Do you do anything omega?" Steve asked. "You smell like an alpha. You act like one. You... you sass like one."
Tony shrugged. "Well, I have a self-lubricating ass, if that's what you mean. And what's your problem? Captain America's an alpha? After all the 'Omegas Can Be Leaders Too' crap you fronted?"
Steve bristled. It was true: he'd been the face of an initiative during the war to promote omega rights, and he wasn't even an omega. He was equal parts ashamed and proud of it.
"Well, you're stuck with me, Tony. And I'm stuck with you. So get used to it."
Tony snorted and looked out the window but didn't deny it.
It wasn't until Tony had a heat that they actually did anything more than argue or snipe at one another. It was during a team meeting with Fury when Steve felt something nudge his leg. He looked over and Tony was looking at him with an odd expression on his face. He still couldn't smell anything but realised what the problem must be pretty quickly. "Sir." He blurted. "I think I just heard someone... calling for help. I.. need to go. Tony?"
Tony, the jackass that he was, feigned confusion, but relented. "Sure.. I'll help you, Cap," he said, cocking a ‘what is it with this guy?’ eyebrow at the rest of the group.
Steve rubbed his stomach as he left so they'd think he was suffering from heat-cramps and Tony pushed him out of the door.
In the car back to the tower, Tony was beginning to sweat. He pulled off his jacket and loosened his tie.
"You still don't smell of anything. How?"
"Pheromone neutraliser. I use a,” he waved a hand, “cologne to smell alpha."
Steve nodded. He was attracted to Tony in that he'd bonded with him and wanted him out of some sense of duty, but with no omega pheromones he was hardly raring to go.
"Oh god," Tony ground out, clawing at his stomach.
"What do you need me to do?" Steve asked, even though he knew what he wanted, but there was no way he'd let his first time with his actual bond be in the back of a car.
"Just, get me home and then - nngg - fuck me, ok?"
It wasn't til wetness began to seep through Tony's pants and Steve finally sensed some of those pheromones that he too began to get hazy himself. Whereas he'd been reticent to touch him before, he pulled Tony into his lap and rubbed his hand on the wet fabric between his legs, bringing his hand up to smell it. "Why do you cover this up?" He closed his eyes and drank in the heady aroma.
"Why do you think? You know how much -ah!- shares would go down if they knew an omega was in charge?"
Steve wasn't listening, nostrils flaring and eyes still closed. "I'm gonna make you stop taking that stuff. Want you to smell like this all the time."
"Ok." Tony agreed instantly, frowning at himself as soon as he'd said it like he didn't realise he was speaking til the words had come out.
Eventually they got back, Happy remaining in the car as Steve carried Tony out and up in the elevator. He'd only briefly been to Tony's rooms once, when he was trying to figure out exactly what his place was in the tower besides being Tony's alpha-pretending-to-be-his-omega. Now he marched through it like he owned the place, tossing Tony onto the bed before tearing off his sodden pants.
"Please," Tony begged on all fours, curving his back and lowering his head submissively. Steve had been hard since the car. As soon as his own pants were off he plunged right into Tony's wet gaping hole.
"Shhh, shh, I've got you. I've got you now." Steve cooed at Tony, brushing his hair out of his face. Tony mewled in response.
Steve leaned down over him and wrapped his arms around Tony’s hot body, whispering in his ear as he began to fuck into his slick hole. "Does it feel good? Having your omega fuck you?"
Tony huffed and elbowed Steve in the ribs. "How does it feel fucking your alpha?"
Steve bit his lip. "Tight. Hot. Really great, Tony. I'm gonna knot you so tight."
Tony whimpered back at him. "Yeah? Knot me up like a little omega slut?"
"That's right. All day long. You gonna take it?"
"Yeah. I want it. Please?"
"You ever been knotted before?" Steve asked, pushing his weight down onto Tony and pushing the air out of his lungs. Tony couldn't move and just squeaked "no" quietly. Steve grinned to himself. "Is that so. I like that." Tony moaned in pleasure at the praise. Steve smiled to himself wickedly realising how much it tortured Tony to be treated like a true omega after all these years.
"Are you going to be good for me, Tony? Do everything I tell you to?" Steve let his weight up off of Tony so he could respond. He nodded his head and whimpered in obedience.
Steve wondered how Tony had ever got through his heats before, if he'd never been knotted by anyone. He supposed he'd have to find out later, once they were done, or in between sessions at least.
Steve reached between where his cock slid easily in and out of Tony to gather some of the slick wetness just to breathe it in, drink in the scent of his omega. "So good, Tony. Perfect, you smell so delicious. I want you."
"You- yours." Tony panted.
Steve pulled out and flipped Tony over even as he was moaning at the loss, "Shh shh, I'm here, don't worry," then plunging back in and watching Tony's face as he did so. It was like he came every time Steve thrust, his eyes rolling up in his head and his jaw slack. Beautiful, he thought. "Mine." Steve said to himself.
He fucked him like that as Tony got looser and looser beneath him, finally getting what he’d craved for all his omega-virgin years. When Steve offered his fingers up to Tony he sucked on them hungrily.
"Tony, I'll knot if I'm not careful, are you-"
"Yeah! No it's fine. Please. Oh please, I want your knot, Steve, please," Tony sobbed.
"Are you sure?"
"Yes!" Tony yelled, slamming his fists into the bed. Steve pulled out to flip him over again and as soon as he pushed back inside he felt his knot begin to swell. Tony felt it too, arching back into it to push Steve deeper.
Steve thrust shallowly a few more times before he really knotted out and couldn't move anymore, Tony breathing in little short huffs and moaning at even the slightest movement. Steve leant down on top of Tony and bit his neck, pleased with the very slight omega tang of the sweat there. Tony whimpered and clamped down on Steve's thick knot and Steve came, pumping deep inside Tony's body to tiny cries of "yes yes yes".
Tony yowled when Steve rolled them so they lay side by side, wrapping his arm around Tony to steady him. "I don't want to crush you! Shh, it's alright, you're fine, ok?" Telling him that he was ok seemed to do the trick and Tony calmed down, threading his fingers with Steve's even as Steve reached lower to jerk him off. It wasn't really a requirement and in a less feverish moment Tony might not have allowed it, Steve sensed, but as he was, impaled upon Steve, he merely took it. His limbs tensed as he got closer to orgasm, but it wasn't til Steve shifted to thrust the bulge of his knot painfully back and forth a few times that Tony came with a cry, clamping down on Steve and milking the last drops of Steve's release out of him as he came all over their hands.
Steve brought his hand up to lick Tony's cum from it, making Tony whimper and laugh all at once. Steve supposed it was rather an old fashioned gesture but he didn't care. Once he was satisfied he bit Tony's neck again and held him tight.
"Mmm, Tony that was... I knew bond sex was meant to be good, but..."
"Yeah," Tony replied weakly. Steve's knot throbbed when Tony spoke and it made him make a little keening sound.
"You feel so perfect around my knot, Tony. So tight."
Tony seemed trapped between insolent refusal and omega obedience when it came to accepting and replying to Steve's compliments.
"You can say it, you're mine now. My omega. Does it feel good?" It was unusual for Steve to be so forthright when it came to sex but for the first time in his life, it all felt so right and correct. His bonded mate safe in his arms with his knot nestled inside him where it belonged. Tony still didn't respond but Steve ran his hand through Tony's hair soothingly, kissing all the places on his neck he could reach without shifting him too much and hurting him.
"Tell me you're mine, Tony," Steve gently demanded and Tony could do nothing else but nod his head. "Y-yours." Steve felt pride and ownership wash over him and he couldn't help the throb of his knot again. Tony whined and elbowed him in the ribs. Steve just chuckled and nuzzled into Tony's neck a little more. The reactor hummed beneath his forearm and he was never so glad of it's existence - that it had brought his Omega all the way to him through ice and deserts and death.
They lay there for a long while before their first rut was over. Both of their minds cleared a little, just long enough for Steve to rummage through Tony's kitchen and make a plate of sandwiches. He brought a big glass of coke which he neglected to add anything other than ice to, despite Tony's instructions for the bar yelled from the bedroom. Steve sat next to his mate, offering Tony the plate.
"Really? One plate? You really are a hundred years old."
Steve ignored Tony's age jibe as he'd taken to doing shortly after their first meeting. "Eat." He ordered and Tony sighed, wincing as he sat up to obey. He rolled his eyes at the single glass of coke. "Could have just had takeout." he said, mouth full of ham and bread.
"There should be at least something traditional about this whole thing," Steve replied. Tony just shrugged.
"Are you sore?" Steve asked when Tony winced again as he reached for the coke. Steve passed it and took a sandwich for himself.
"What do you think?" Tony replied sarcastically. Steve huffed.
"What? Not proper omega manners? Newsflash big guy, you're hardly one to talk."
It was Steve's turn to roll his eyes.
"Listen, we might not have chosen this - each other. But we're bonded now, ok? And I'm going to knot you as and when you need it," Steve promised, not without a shade of threat in his voice. It was different to his Captain America voice. This was much darker, and it sent a jolt through Tony and made his sore entrance throb with want once more.
Steve's nostrils flared again and Tony could tell he could smell how wet he was getting, how the cramps would start again soon and he'd be begging for the sweet hot relief only Steve could give him. He took the plate away and crawled over Tony, the underpants he'd put on to go to the kitchen now tented obscenely.
Tony began to turn over but Steve pushed him back down with a hand on his shoulder. "No, I want you this way so I can see your face as I knot you. Watch your mouth as you tell me you're mine. You want that." Tony hated that he had no control over how wet he was becoming just at Steve's promises and how thick the scent of his alpha was in the room.
Steve pushed Tony's legs open and pulled them up, slotting himself between them and letting them drape over his knees as he slid easily back in. Tony cried in relief as the empty space inside him was filled. Steve sucked marks into his neck as he gave him what he needed, what he craved. It felt better this second time, the itch deep within Tony being scratched slower now, so he could really take in just how delicious it felt. The relief and the comfort of Steve - stick in the mud, snotty do-gooder Steve - crowding over him and promising his knot. Promising to take care of him and give him exactly what he needed always.
"What do you want, Tony?" Steve asked, looking down at him with those shiny red lips and blue eyes which had looked so innocent before and so flushed and dirty now. Tony looked up at him and gave up any pretence, honestly answering, "Your knot, Steve. I want your fat fucking knot deep inside me til you've pumped me full of your sperm and made me yours forever."
"You're already mine forever, Tony."
"I know." Tony nodded. "You gonna knot me again?"
Steve mouthed 'yuh huh', cupping Tony's jaw and rubbing his thumb across Tony's bottom lip. Tony opened immediately and sucked it in, pleased to feel Steve's cock twitch inside him.
Steve's thrusts grew erratic and hard, the head board slapping against the wall and Tony crying out each time. Steve bent over Tony to scoop his arms beneath him before pushing in as hard as he could before his knot swelled, pulling him up and into his arms as Tony went limp and he pumped his thick load into him.
Tony turned his head away to let out a sob of pain-pleasure, feeling Steve’s possessive gaze burning into him. He moved again, the knot too much inside him and he felt himself come untouched between them.
Steve braced himself above Tony and kept staring at him til he relented and looked back, felt bathed in, ugh, love, when he met Steve’s eyes. Goddamn hormones. He hated the smug bastard, but the world could have ended right then and he’d have been happily held there in the tractor beams of Steve’s eyes. “Mine,” Steve said again, the word making Tony’s skin quiver. “Yours,” he felt himself say, and then Steve was kissing his neck again and he’d have to buy some turtlenecks at this rate but by god that felt good.
The process was repeated a number of times until they were both utterly fucked out. They lay, sticky and exhausted in one another’s arms, Tony trying desperately to cling to the fact that he really didn’t like this guy all that much even though that was being shorted out by how special and safe he felt under Steve’s great big hands.
“It’s a good job you’re on suppressants, the amount of come I just put inside you, Steve murmured. “There’s no way you couldn’t get pregnant after that,” he said, brushing a finger up the crack of Tony’s ass. Tony shivered in his arms.