Some alphas would take one look at Tony and declare that a good knotting would knock him down a few pegs. They'd be wrong, though. He's been knotted plenty of times and he's been in charge during every one of them. Tony's just a dominant omega and that's the end of it.
Steve is a bit dismayed, at first, about how submissive Tony isn't. In his day, omegas were submissive and alphas were dominant. It was in their nature. But apparently it's not in Tony's. It's not like he's suppressing it, either, as Steve's found out. The first time Steve tries to dominate him, Tony laughs in his face.
They've just finished a mission debriefing when it happens. Everyone else has already left except Tony and Steve, Steve because he likes to be the last one out and Tony for reasons that become pretty damn clear when he stands up. He's got a hand pressed against his arm, and Steve feels alarm when he realizes blood is dripping out from between Tony's fingers.
"Stark," he says, and guilt makes his voice comes out rougher than he means it, because he should have noticed before now that Tony's injured. "You need to be in medical."
"It's a scratch," Tony tells him. He looks like he wants to wave Steve off, but his hand is otherwise occupied holding his blood inside him, so he shrugs instead. "I'm fine, Cap."
"Tony," Steve says, and he uses the most dominant tone he has. He doesn't approve, exactly, of alphas who use their power over omegas to get what they want, but Tony's hurt and he needs to be in medical. If he won't go there on his own, Steve will use any advantage he has to do get it done. It's in Tony's own best interest.
"Nice try, Capster," Tony says, already walking away. "But I'm just not that kind of girl."
Submissive omegas do still exist, Steve knows. Clint, for example. The guy's mouthy out in the field or when they're all together, but Steve's seen him interact with Coulson enough to know he's got to be as submissive as any alpha could want in the bedroom. Tony's not like that, though. His attitude isn't a front or a separate aspect of his personality. It's in every single part of him.
Steve's heard stories about Tony to back all his theories. When his father died, the board was hesitant about declaring an omega the CEO of Stark Industries. Tony was able to change their minds through sheer force of will and persuasive charisma.
It's not just his mind that's powerful, either. The first and only time an alpha tried to knot him against his will and show him his place, Tony put him in the hospital with a broken wrist and chemical burns. No one fucks with Tony because he just won't stand for it.
That's not even going into his kidnapping in Afghanistan. No one ever thought an omega could come out of that situation alive and unbroken, but Tony proved them wrong. Tony doesn't talk about it, but Natasha seems to think the men who held him implemented some kind of water torture against him. Based on Tony's occasional flashbacks that Steve's been witness to, she's probably right. But the very fact that Tony managed to not only escape, but also create something as amazing as the Iron Man suit under those conditions really speaks to the testament of his strength and will power.
It's possible that Steve's being forced to reevaluate his ideas about omegas.
Eventually, the tension between them blows over. Steve never tries to dominate Tony again after that first time in a meeting, at least not directly, and Tony, in turn, stops being so prickly about the times Steve does assert his rank over the team. Tony's still infuriating at times, going off on his own, doing whatever he wants, not communicating with the rest of the team when he's about to do something tremendously stupid and suicidal. Still, it's getting better.
Sometimes, Steve even thinks there might be something between them. It's nature, he knows, alpha and omega go together, but with Tony's it's never really like that. Tony's coarse and unrefined, even when he's wearing suits worth more than Steve's entire apartment growing up. He swears and tells dirty jokes, walks about half-naked in public. He's the farthest thing from an omega Steve can think of in so many ways.
That's why it's so confusing, at first, the attraction between them. Tony flirts with everyone, but he concentrates his efforts on Steve, and Steve, for reasons he doesn't even really understand, flirts back. He doesn't know where it's going for the longest time, different as they are, but he keeps going with it, because, despite everything Tony is and isn't, it all feels so right.
Tony's done wonders for omega rights. Sure, the big portion of rights were granted in the '60s while Steve slept, and he remembers the suffrage movement in the twenties, but things still aren't really equal in practice. They say the average omega only makes 80 cents for every dollar an alpha makes. But Tony doesn't take anyone's shit, regardless of gender, so he's a great spokesman for the movement. He's also an equal opportunity employer. On top of all that, he donates a ton of money every year to omega rights groups.
Sometimes, when they have to do meet and greets for the team, omegas come up to Tony. Some are kids, eager for advice on how to make it in an alpha's world. Others are adults who are all so grateful for what he's done for the gender. All of them are in awe of him. Steve knows Tony appreciates the comments, and not just to feed his ego, either. Tony likes to know he's doing good work, saving the world, one omega at a time.
And sure, he also gets alphas making lewd comments or journalists asking him sexist questions, but a raised eyebrow usually intimidates them into silence. If it doesn't, Tony takes the opportunity to embarrass them. The man's brilliant at turning a conversation his way.
The way they end up in a relationship is this: after months of living together and working together, Steve realizes he doesn't even think of them that way anymore. They're not alpha and omega, they're Steve and Tony, and they've been flirting, more and more every day. Sometimes Tony's very obvious about it, about his want to get Steve into bed. These days, though, Steve doesn't blush when he does it, doesn't think that an omega should be more delicate, more refined. He remembers having those thoughts, once upon a time, but these days, they don't make sense in his head.
So when Tony looks at him and says, "Hey, Cap, my heat's coming up. You wanna see me through it?" Steve can't do anything but nod shakily.
Steve's never been with anyone sexually before, let alone seen anyone through a heat, but he has a vague idea that he, as the alpha, should be in charge. In the porn he's watched since coming to the future, always alone in his room with the doors very firmly locked, the alphas are always the ones in charge. They lay the omegas out flat, make them beg for their knots, and the omegas are always perfectly happy to do so, desperate for it by the end.
With Tony, it's different.
"Come on in, Cap," Tony says when he opens the door after Steve knocks. Steve can tell he's sweating as soon as he gets a look at him, but it's not until he has to step past Tony to get into the room that he actually smells him. He's smelled it before, of course, because accidents do happen and omegas occasionally get caught out and about when their heat starts, but he's never been this close to one.
"Wow," Steve says, and leans close to Tony, not even caring that the door is still wide open. "You smell…." He can't even finish the thought, just inhales shakily. The arousal floods to all parts of his system, and he wants nothing more than to just pin Tony to the wall and take him, mark him, knot him.
Tony holds up a hand, and Steve realizes he's been advancing, crowding Tony back against the door. "Why don't you have a seat," he says, more command than question, indicating the bed.
Steve pulls back, then, gets control of his instincts. If he ever wants to do this with Tony again, and he absolutely does, so much, he's going to have to play by Tony's rules. He goes to sit on the edge of the bed and watches intently instead as Tony closes and locks the door, then strips out of the clothes he's wearing. His skin is flushed all the way down his chest, but he's got a dark complexion, so it's not as bad as Steve imagines his own skin is right now, just from the pheromones in the room.
"You can get naked," Tony says, laughing and Steve blushes harder, not just because he's being ordered around by an omega, but also because of how turned on he is by it. He stands and fumbles with his sweats. He'd worn loose clothes today, just in case, but the way Tony looks at him as he takes them off makes him think it's what's underneath that counts, anyway.
He sits back down on the bed when he's done, scooting up into the center, and is rewarded by Tony sauntering up him, as comfortable naked and in heat as he is fully clothed in his lab. The scent gets stronger again as Tony gets closer, and when Tony climbs up into Steve's lap, it becomes nearly unbearable. His skin is hot to the touch, and Steve can't help but nuzzle into his neck, soaking in the pheromones. This close, Steve can also feel how heavily he's breathing.
"Tony," he moans, overwhelmed, and Tony kneels up, spreading his legs, one hand braced on Steve's shoulder.
"Feel how wet I am for you," he says, grabbing Steve's fingers and dragging them back to feel there at his entrance. It's true, he's soaked, the slick gushing out of him, running down his thighs. Steve's surprised he hadn't felt it whenever Tony was in his lap, but then, he had been pretty preoccupied by the scent of the heat.
He takes the initiative whenever Tony lets his hand go, slips two of his fingers inside the wet heat. Tony's body parts for him easily, and Steve runs on instinct and knowledge from porn, slowly withdraws his fingers before slamming them back in. Tony arches and gasps, so Steve does it again and again.
"Curl your fingers," Tony tells him and Steve does, repeats the thrusting motions like that. It takes a few tries, but he finds what Tony's trying to show him, that spot that makes Tony cry out with every pass across it.
Steve wishes he could say something, tell Tony how hot he is, how much he wants to knot him, breed him, fill him up with Steve's pups. He gets as far as, "I-I want…" before he trails off, lost again in how amazing this is, to have Tony like this on top of him.
Tony smiles at him, but it's strained and his breathing has become ragged gasps, now. "Let's get me knotted before I die of sexual frustration, yeah?"
Steve's hips jerk up at the words and he manages to get his fingers back out of Tony. He brings them up to eye-level to inspect. The slick is running down his entire hand, and it smells so good Steve can't help but take a few licks. Tony groans at the sight, head dropping back for just a moment.
Steve goes to roll them over, get Tony under him and Tony's head snaps back up. "Wait," he says, gripping both of Steve's shoulders tight. "Just like this." He pushes Steve to lie back, then reaches behind him and grasps Steve's cock, giving it a few strokes. In one smooth motion, he sinks down onto it.
"Guh," Steve says, eyes rolling back into his head and hips pushing up in little stuttering thrusts. It's everything and nothing like he imagined, hotter and wetter and tighter than around his fingers, somehow, and so, so amazing. He feels the tingles at the base of his cock that mean he's going to knot, and it takes everything in him not to just go with the feeling. He wants to be Tony's best, though, the best alpha who's ever knotted him, so he holds out, tries to think of the nuns at the orphanage or trench foot, but none of it works.
Tony starts a fast pace right off the bat, lifting his hips and slamming them back down, taking Steve as deep as possible and crying out with each thrust down. Steve's hands find his hips, not to control the pace but just to hold on, to have another point of contact with this amazing omega.
It doesn't last long, like that, not with Steve on the edge already. He pulls Tony down hard against him as his knot forms, holds him there and comes. Tony doesn't seem to mind, though, just grinds down against Steve's hips and brings his hand up to pump at his own cock. He comes a few seconds after Steve, though Steve's orgasm lasts much longer.
"That was amazing, Steve," Tony pants as he comes down. "I didn't think you had it in you."
Steve wishes he could make a pointed comment right now about what Tony has in him but he can't find the words. He just shivers and clings every time a new wave of orgasm rolls through him. Tony waits it out on his lap, just rides high through the long, long minutes Steve's still inside him.
When they finally separate, Tony curls against him, absolutely filthy with cum and slick. Steve doesn't care, just wraps an arm around him and pulls him closer.
"Next time," Tony tells him sleepily, worn out from the aftereffects of the dissipating heat, "you can be on top."
That's fair, Steve guesses. The next wave of the heat will probably be in a few hours, and then Steve can try his luck at knotting Tony from behind. Then it will be Tony's turn again, and Steve can't wait for that, either. It's not how he thought a heat would go, but with Tony, it's absolutely perfect.
They start doing something like dating after that. It's sexual, certainly, though not just that. They go out together, to movies or restaurants. People take pictures of them with their phones, post them on the internet, with headlines like, "Tony Stark: Finally Forced to Settle." Steve knows the truth, though; he could never force Tony into anything.
Sometimes, he wishes he could, for the same reasons he's always wanted to: not to assert his alpha dominance, but just because he wants Tony to take better care of himself. Eventually, after months of trying to use his alpha status like that, it occurs to Steve that maybe he's going about it the wrong way. If Tony can't be forced, perhaps he can be persuaded.
"Tony," he says one night after Tony's been in the lab for far too long to be healthy, "come to bed. I'll make it worth your while."
It's sneaky and yet so very obvious, and Tony folds like a cheap suit. This is nothing like Steve would ordinarily say or do, using sex in that way, but with Tony, it's never just about sex. There's emotion between them, something not quite love, but it's certainly getting there. He likes Tony, seriously a lot, and he wants to take care of him. He just knows now that the solution is nothing to do with their gender and everything to do with them as people.
Steve gets questions, sometimes, people asking him how he controls Tony Stark. The answer, of course, is that he doesn't do any such thing. Their relationship is give and take, a partnership of equals, and that's just how Steve likes it.