Archive of Our Own

1. Physiological Synchronization in Self-Proclaimed Soulmate Pairs. 1944.

The existence of so-called 'soulmates' has long been a topic of anthropological and sociopsychological research. Here, for the first time, the phenomenon was studied with methods of the natural sciences. Serial measurements of pulse, blood pressure and respirations were collected with the subjects adjacent to either their partner or an unfamiliar test subject. In seven out of ten couples that participated in the experiment, a synchronization of vital signs was observed when subjects were paired with their 'soulmate', but not when paired with a subject unfamiliar to them. The results persisted when the test subjects were blinded to the identity of the person next to them. These physiological alterations may be implicated in the strong feelings of partnership experienced by self-identified 'soulmate' pairs.

"You hear that, Cap? I told you! It's not just a thing out of romance novels," Howard announced, his flashy grin particularly triumphant. "There's science! There's solid evidence right here!" He tapped at the science journal on the table in front of him with his index finger.

Steve shook his head. "Seven out of ten couples. Is that supposed to be convincing?"

"You know how rare these couples are, right? They probably had to comb through the entire population of California just to find these people," Howard pointed out defensively.

"Still. I'm not impressed," Steve said. "Besides, why are they even wasting time on that nonsense when we're at war?" He motioned at the mess tent around them, as unnecessary as the reminder was.

"Hey! It's not nonsense!" Howard complained. "They're using perfectly valid scientific methods. You can't put all basic research on hold because of the war, or we'll regress back to the Dark Ages. Anyway, isn't this what we're fighting for? We need the world to be peaceful and safe again, so we can go home and be with the people we love. Maybe have a chance of finding those soulmates."

Steve crossed his arms. "I'm not fighting for some fairytale perfect match that I've got a one in a million chance of meeting."

"Many experts think they might be much more common than that," Howard returned, as if he'd completely missed the point Steve was trying to make. Knowing him, he was doing it on purpose. "If we knew more about the phenomenon, it could be different. If we could understand why some people match, then maybe we could find all the matches that go undiscovered—it would change everything. That's why studies like this are important." He picked up the journal, shaking it at Steve.

"Are we doing this again?" Steve growled. They'd had similar conversations before, and out of the many times he'd come very close to punching Howard in the face, these were some of the closest. "You're saying that couples that don't match on some mystical level are inferior. Well, chances are that soulmates aren't even real and this is all in their heads. Maybe there isn't that one perfect match for anyone. Even if there is, that doesn't make them better than the rest."

Howard dropped the journal on the table and raised his hands in surrender. "No, no, that's not what I'm saying! All love is important. No one knows that better than I do, I've loved lots of ladies in my day!" he said hurriedly. "I'm all for everyone getting together with whoever they want to, it's all good. I'm just saying, if there were someone out there you could have this special connection with, wouldn't you want to know?"

Steve already had a connection with someone. He loved Peggy, even though he hadn't found the courage to act on those feelings yet. It never seemed like the right moment. They were always on some mission, or crossing paths between assignments. There was too much going on to think about proper relationships. The last thing he wanted with her was some kind of hurried and meaningless wartime fling. She deserved so much more than that. If he ever got together with her, he wanted it to be serious.

As important as Peggy was to him, he didn't think they were soulmates. He did feel different when he was close to her, of course he did. He got nervous and awkward, all his insides twisting into knots, and worried he'd say something stupid. He envied Howard for how effortlessly charming he always seemed to be, no matter whose company he was in. Still, he didn't feel any kind of a mystical connection, like they described in those soulmate stories. He didn't feel like he was one with her, like they were sharing each other's feelings, or like they somehow breathed in synchrony, like this most recent article suggested. He couldn't even begin to imagine how that would feel like, but he was pretty sure he wasn't feeling it.

Steve had heard everything about the theories Howard was so fascinated by, because Howard was always eager to share them. For all his womanizing, Howard had a surprisingly romantic streak. He often made tongue in cheek remarks about trying to meet as many ladies as he could so that he'd maximize his chances of finding the right one, but clearly, considering how much he talked about soulmates and how much thought he must've put into everything related to them, the topic was important to him.

Howard had told Steve some scholars thought there were many more soulmate pairs out in the world than the lucky few who had found one another. There might even be someone for everyone, but if these people were randomly distributed across the world, most of them would never meet.

Steve wasn't sure he liked the idea very much.

He'd grown up thinking soulmates were a fairytale thing that some people took too seriously. His mother hadn't believed in them—she'd considered them as unrealistic as people who claimed to be able to heal others by laying hands on them or those who said they could talk to the dead. Sure, some couples claimed to be soulmates, but most likely they were no more special than anyone else. Love was many things, she'd told him, but it wasn't magical. Relationships were something you had to work at, not something that happened because you were meant to be together with someone. He thought that had been very good advice.

He hadn't given the whole soulmate thing very much thought before all these conversations with Howard. Before he'd become Captain America, he'd thought he'd be lucky if he found anyone who'd even look at him twice. Now that he was suddenly receiving plenty of attention and Howard kept going on about soulmates, he'd actually considered the question, and come to the conclusion that the idea of some predetermined partner felt too much like arranged marriage to his liking. He didn't really want it to be true.

Steve knew Peggy's views on soulmates weren't too different from his own, even though she was much better informed on the topic than him. She'd explained to him that the theories Howard liked to cite were dismissed by most other scholars as 'poppycock', as she'd put it. Most of the research was done by people who already thought soulmates were real, she'd pointed out, so it wasn't exactly impartial. As for her own opinion, she'd said she might start believing in them if she actually met hers. Clearly, she didn't think she already had, so whether she liked Steve or not, she didn't think they were soulmates either.

"Come on, it's just a thought experiment," Howard said, when Steve still hadn't answered his question. "Imagine there was a way to know for sure whether you've got a soulmate, and who that is, if you do have one. You'd be curious, wouldn't you?"

If it turned out that Howard's favorite theories were right after all and there actually was someone out there who'd make Steve feel like the stories said, someone who wasn't Peggy, would he want to know? And if there was an imaginary lady who was, through will of God or quirk of fate, somehow connected to him, would it be wrong for him to resist that? Would he inevitably fall in love with that person?

"Of course. Who wouldn't be," Steve admitted. "Still, I think I'd just like to take my chances instead."

If there was a soulmate for him out there, someone he was somehow meant to be with, surely he'd also be meant to meet her.

Soulmates weren't something Steve spent a lot of time thinking about. He had plenty of other things on his mind, things that were actually important, unlike some fringe theories about romantic fairy tales. The occasional, brief conversations with Howard were certainly not enough to sway his opinion.

He did spend a lot of time thinking about Peggy. He missed her when she wasn't around, and when she was, he always got all too flustered. He could face the enemy's armies without blinking, but somehow, when it came to her, he just couldn't take that one step; couldn't say those few words that it would take to let her know how he felt.

And yet, somehow, in his final moments, watching the ice rush inevitably closer, amidst all the regret that he had missed his chances of ever being anything more than friends with her, there was the stray thought that maybe this was always going to happen. Maybe soulmates were real, after all, and this was why he hadn't been hers.

As the freezing cold engulfed him, darkness creeping into his vision, he thought that maybe, with him gone, she would meet the person she was meant to be with, and live a long, happy life.

2. First Genome-wide Scan of Persons with Synchronized Physiology Reveals No Strong Candidate Loci. 2003.

Many studies have reported intriguing evidence for the existence of couples whose partnership extends beyond usual physical intimacy. These couples, colloquially termed 'soulmates', appear to be bonded on a physiological level. They have been estimated to represent some 0.5% of all intimate relationships in Western countries. Despite decades of research, a biological mechanism underlying the phenomenon has yet to be uncovered. As there is some preliminary evidence for heritability of this trait, we performed a genome-wide scan for 26 families, including a total of 103 subjects, 39 of whom report being in a relationship with their 'soulmate'. Our results did not reveal any consistent candidate loci. However, it must be noted that not all those who have the predisposition for a synchronized partnership will have found their counterpart, and as we did not perform any testing to verify the self-identified partnership status of our subjects, some may not in fact represent true 'soulmates'.

"See, flyboy? They've finally done the impossible and solidly proven a negative," Tony said, swatting the table in front of Rhodey with the article he'd printed.

"You're late," Rhodey told him, not looking at him but going straight for the paper. He grimaced when he saw the title. "Oh. Soulmates. I thought this was going to be something relevant to my interests."

Tony sat down opposite to Rhodey and waved at the waitress for coffee. "I know you're interested, no point in pretending otherwise."

Everyone had some kind of an opinion on soulmates. That was a fact. Tony wouldn't believe anyone who said they didn't. Not to mention that he and Rhodey had debated the topic countless times in various states of inebriation. He knew Rhodey was an agnostic in the matter, reserving judgement in case someone managed to come up with smoking gun evidence.

Tony's own stance was the only reasonable one: that it was all nonsense, like every other bullshit paranormal idea out there. Studying these things was a waste of time and money. This had been Tony's opinion since he'd been old enough to understand the concept. His dad's ridiculous beliefs had fueled the fire of his annoyance. Dad had always said he and mom were soulmates. Mom had played along, but Tony had never been sure whether she'd believed it or not. Whichever the case, a fat load of good that had done to them. From Tony's point of view, his parents had been miserable together.

Dad had probably fallen for the soulmate bullshit so hard because it'd been a handy explanation to a lifetime of failed relationships: they hadn't worked out because he'd been meant to meet his mysterious One True Love. Tony had no such delusions. He was well aware he was just fundamentally incapable of lasting commitments. He'd accepted this as a teen, and made the best of it. Who needed commitments, when he could have all the sex he wanted with the prettiest girls and most gorgeous guys the world had to offer, right?

"Even if I were," Rhodey said, raising his eyes to cast Tony an unimpressed look, "this wouldn't prove anything."

"Oh, come on, it won't get much better than this. It's a decent-sized study in a respectable journal and all. Not easy to pull off when you've got a negative result," Tony pointed out.

"Do you even know enough genetics to understand what they did?" Rhodey asked suspiciously.

Tony shrugged. "It's not like it's particle physics."

"My point exactly," Rhodey said, smirking at him. "At least I'm humble enough to admit that I've no clue. Genome-wide scan? Candidate loci?"

"As a matter of fact," Tony began, but the waitress finally showed up, saving Rhodey from Tony's best take on Modern Molecular Genetics for Dummies. Not that Tony was about to complain; this also meant that he finally got his coffee and put in an order for a pile of eggs, bacon and pancakes. After last night's party, he needed some salt and grease with his caffeine. Which made this exactly like most mornings in his life.

"Anyway," Rhodey said, "My point still stands: this is one study, with a limited number of participants. It's not enough to say anything for sure."

Tony waved a forefinger at Rhodey. "See, that attitude is why they've kept at this for decades, no matter how flimsy the evidence. The nutjobs who believe in this wouldn't be able to get funding if not for all the undecided folks. Since there are enough people who're on the fence, they can always get a grant from here or there, and so they keep going. It's like perpetual motion." He waved his hand around in a circle. "If you could harness human gullibility as a power source, you'd have unlimited free energy."

Rhodey raised his eyebrows, a smirk playing on his lips. "You know, Tones, for someone who thinks this is nonsense, you always seem awfully invested in it."

"Yeah, yeah, dad's obsession, reverse psychology, blah blah. Please spare me the pop psych, it's way too early for that," Tony groaned, going for a large gulp of coffee.

"It's past midday," Rhodey reminded him.

"Not in my time zone," Tony said. "The thing is, it doesn't matter what I think or what anyone thinks. If there was a soulmate gene, they would've found it in that study. They didn't. I'm sure there will be a couple more papers repeating that result, eventually, but they'll just say the same thing. There isn't one. End of story."

3. Identical Non-Coding Sequences in the Genomes of Persons with Synchronized Physiology. 2008.

To conclude, our results suggest that the unique traits seen in physiologically synchronized couples could be related to an identical, nearly 1000 base pair sequence of non-coding DNA, several repeats of which were found in both subjects' genomes in our study. Nothing resembling this sequence was present in any of the matched control subjects' genomes, implying that this is not a case of normal population variation. Furthermore, none of the other publically available human genomes included this particular sequence. More studies are needed to confirm whether identical sequences can also be found in other synchronized couples.

Tony's life after Afghanistan was, somehow, simultaneously better and worse than it had ever been.

Iron Man was awesome. He loved being Iron Man. He loved the suit, he loved flying, and above all, he treasured the feeling that he was actually, finally, doing something meaningful. He'd never really had that before. It was funny, really. All his life, he'd been one of the richest people on the planet, running a highly influential company, and still he'd felt like he was drifting aimlessly. Now, he was firmly at the wheel, and for the first time, he had some idea about the direction. When it came to his company, that direction wasn't quite fully formed yet, but he was getting there.

It was all good and great, except for the part where he kept waking up every night, drenched in sweat, from nightmares where he felt like his chest was cut open or he was drowning, or where everyone around him was dying because of something he'd done. Not to mention the constant presence of the arc reactor as a reminder of what had happened, and the thought of how fragile it made him. And then there were memories of Obie crouched over him with the cruelest smile on his lips, his eyes cold and merciless. Tony had trusted him. He would never, ever have believed Obie would try to kill him. He tried not to think about it too much, because if he did, he might start doubting everyone around him, and he had to admit he sorely needed the few friends he still had. He couldn't start doubting them too, or he'd go crazy.

As things were, he thought that now that he'd somehow survived all that, things would slowly start getting better again, settle into some kind of a balance. Of course, the universe had another surprise in store for him, instead.

Tony was hammering out a dent from a shoulder plate, courtesy of his most recent mission, when Rhodey called. Since Rhodey was on the very short list of people whose calls he actually tended to take, he picked it up right away.

"Tony? Did you check out the email I sent?" Rhodey's voice came through the workshop loudspeakers.

"You know I get around a hundred emails an hour, I can't possibly keep track of all of them," Tony replied dismissively. "Yours have the highest priority, of course, but I've been busy."

"Well, you should read this one," Rhodey said, sounding even more serious than usual. "You might want to sit down when you do."

"That bad, eh? Can't you just tell me?" Tony asked, intrigued. If it was something really bad, involving death and destruction and the like, Rhodey would've told him right away instead of being all coy about it. Tony had no clue what this might be about.

"Wouldn't want to ruin the surprise," Rhodey returned. "Just read it, okay?"

"Sure thing, porcupine." Tony waved a hand in the air to tell Jarvis to cut the connection.

Patience had never been one of Tony's virtues—not that he'd had many, anyway—and Rhodey's call had made him curious enough that he wasn't going to wait. He sat down at his desk and opened his inbox, filtering it to things Rhodey had sent to him. The message on top of the list had 'I won't say I told you so' as the subject line. The message itself was empty aside from an attached document: a scientific article. Not just any article, though. It was a very high-profile one, published in Nature, and it was about soulmates.

Goddamn. Without even reading it, considering Rhodey's call and that subject line, Tony had a fairly good guess for what it might say.

Tony didn't tend to spend a lot of time reading papers; when there was something particularly relevant to his interests, he skimmed through them, checked out the abstract, maybe glanced at the methods to decide whether they were solid. This one, though, he read from start to finish. Three times. Including the supplement.

It wasn't exactly irrefutable evidence for anything. They'd found a stretch of shared DNA in two people. That was hardly unusual. All humans shared most of their DNA. Heck, humans and chimps shared over ninety-five percent of their DNA, whatever the exact figure was nowadays. Multiple copies of an exactly matching thousand-nucleotide stretch of DNA, shared between two unrelated people who claimed to be soulmates, completely absent from everyone else's genome, though—that was undeniably unusual.

Maybe they'd faked it. Wouldn't be impossible to do. Fraud happened even on the highest tiers of research. Then again, this must've been scrutinized to the max, for the scientists to get it published in one of the most prestigious journals out there.

A key feature of scientific thinking was the ability to admit you were wrong. To shift your paradigm.

Tony had been so sure it was all bullshit, though.

Dented armor forgotten, he grabbed a bottle of bourbon and poured himself one, the article still open on the screens in front of him.

By the time Pepper showed up, there was less booze in the bottle than there was in him, but he was still feeling embarrassingly shaken considering this was all brought on by a paper he'd read. He'd been through months of torture and been betrayed by his mentor, for crying out loud. He was seriously overreacting here. Still, it was what it was. He poured the remaining contents of the bottle into his glass and swirled them around.

"I take it that you heard the news, then," Pepper commented, taking in the scene.

"You know me so well," Tony said sardonically. "You must be over the moon about this, right? You always thought it's such a romantic idea."

"I always thought it's nonsense, same as you," Pepper corrected him. "Although yes, romantic nonsense at that. I'm still not sure what I think, when it's just the one study. The media's loving it, of course. 'Science confirms: soulmates exist' is the top of the news on every channel and website."

"I've got the strangest feeling, you know. It's like I always knew this would happen," Tony said, because he'd drunk enough that his filters were down. "That I was so angry and annoyed about all this bullshit, because deep down I knew it was actually true and dad was right, and I was just waiting for the other shoe to drop."

"That's just a reaction," Pepper said soothingly. "You'll feel more rational about it once you get used to the idea."

"How is it that somehow dad always gets the last word?" Tony complained. "Here's to you, you old bastard. I'm sure you're gloating, wherever you are." He raised his glass and knocked back the last of the drink.

"Tony. This isn't a bad thing, when you stop to think about it," Pepper went on, annoyingly calm and all too positive. "This means there's a better way than random chance for people to find their soulmates, if they want to."

"Exactly," Tony said sourly.

That was the problem, wasn't it? He didn't like the idea at all. He didn't want his love life to be determined by some genetic anomaly. He'd hated the concept when he'd thought it was nonsense, and he hated it even more now that there were reasons to believe it might be science instead.

Take Pepper, for one. Tony didn't get any kind of a magical synchronization vibe from her, and yet he loved her more than he'd ever loved anyone before. He'd give up everything for her. He'd pluck the arc reactor from his chest and hand it out if she asked him to. That had to be worth something, even if they didn't share some random string of DNA.

He should've told her a long time ago. He should tell her now. See how calm she'd be after that. But it was already too late.

"You know what it also means?" Pepper pushed on, because they didn't share a mystical connection, and obviously all she could see was Tony staring mournfully at his empty glass.

Tony frowned at her. It sounded like she was expecting him to catch on, but he had no idea what she was getting at. "That there will be plenty more disappointed people in the world when they realize that finding your soulmate isn't a shortcut to bliss and harmony?" he suggested.

"You read the paper, right?" Pepper checked. "They're theorizing that to catch the soulmate sequences, you'll need to do high-coverage whole-genome sequencing. That's not cheap. We've been thinking about new directions for the company."

"Oh. Oh!" Tony exclaimed, as the penny dropped. "You may be on to something there, Pep."

"Of course, there's no telling how this is going to pan out, but if it turns out this study isn't some kind of a freak coincidence, the biotech industry is going to get even hotter than it's been so far," Pepper spelled out what Tony had finally realized, too.

He had been looking for something non-violent and constructive for his company to do. What could be less violent than bringing lovers together? As much as he still hated the whole soulmate concept, he couldn't deny that it was a brilliant idea. Besides, even if it didn't turn out the way they expected, they could just stick to biomedical research. Not a bad direction to go, either.

"You're a genius, Pepper," Tony declared. "Never let anyone tell you otherwise."

"I hope Jarvis recorded that," Pepper said dryly. "So, I already took the liberty of looking up potential start-ups that we might be interested in, but I think I'll leave that conversation for when you're a little more sober."

"Eh, I'm not that drunk," Tony protested. "No time like the present and all that. Show me."

Within a month, Stark Industries was the proud new owner of half a dozen small to medium biotech companies, and Tony was busy learning all he could about DNA sequencing. It was about as far as you could get from what he had expertise in, but in the end, the technology wasn't that complicated: what it came down to was a combination of chemistry, microfluidics and optics. Of course, there were also the computational challenges of what to do with the genome data once you had it, but that was basically a very large-scale string searching problem, which meant Tony understood it just fine. All in all, he could definitely come up with plenty of ways to improve the tech.

Iron Man by night, genetic match-maker wannabe by day. Who would've thought. His life was so weird now. A lot of the time, he actually liked it.

More scientific articles soon followed the first one, confirming the finding: it was an irrefutable fact that there were pairs of people in the world who had repeated shared strings of nucleotides in their genomes that no one else had. Those same people also experienced this mysterious, but very much measurable, connection when they were in one another's presence. Since Persons with Identical Non-Coding Sequences was a mouthful, it morphed into PINCS. Tony was sure the scientist who had first come up with the original phrase cringed every time the cutesy acronym was used.

They really had played their cards well in this, putting Stark Industries in prime position to become the market leader in a new burgeoning field.

Tony included samples from his mom and dad among the first test runs of their pipeline. The result was a loud and clear positive match. They really had been soulmates, then, no doubt about it. He raised yet another toast for dad that night.

Something Tony realized early on was that there'd be some serious cognitive dissonance involved if he went around alternatively posing in armor and waving a pink flag for soulmate pride. Iron Man was very much one of the good guys and certainly supported peace, love and happiness in all shapes and forms, but he did also make stuff blow up a lot. Iron Man wasn't the ideal poster boy for Stark Industries' new Amoromics division—another neologism that had become common use and that Tony struggled to pronounce with a straight face. Tony had already gone and told the world he was Iron Man, and couldn't take that back even if he wanted to. Besides, he didn't want to. He loved being Iron Man.

Also, he still hated the whole thing, science or not.

Luckily, there was a good solution to the issue, and her name was Pepper Potts. Pepper already had a positive attitude towards soulmates, she was the mother of this whole idea anyway, and really, Tony thought her gig as his PA didn't let her use her full potential. She could be the fresh and stunningly beautiful face for the new, benevolent Stark Industries. It was a perfect match.

As for the two of them—Pepper never asked Tony whether he wanted to test if they were a match. He didn't bring it up, either. It was obvious enough that they weren't. No need to rub it in.

4. Revised Estimate of the Worldwide Prevalence of Matching Identical Non-Coding Sequences. 2012.

Databases containing genome information for the purpose of matching Persons with Identical Non-Coding Sequences (PINCS) have become a global phenomenon. These databases range from centrally administered national registries to local and multinational commercial operations of various sizes, with different levels of accessibility for research purposes. We collected anonymized information of the numbers of subjects and successful matches in 57 different databases from 34 countries. Taking into account the percentage of population covered by these databases, we used a Bayesian approach to calculate the expected overall global prevalence of matching sequences. Our revised estimate is that a total of 65% (95% confidence interval: 62.3–67.7%) of the world population are likely to be PINCS.

Steve woke up to find himself in a world that was completely different, yet somehow very much the same as what he was used to.

New York wasn't entirely unfamiliar. Sure, it was bigger and flashier, cars looked a bit different, and clothing styles had changed and gotten more varied, but he would've still recognized it as his city without a moment's hesitation. Then again, some things had evolved beyond the wildest, most futuristic visions Steve remembered from the past, like computers and telephones. In fact, telephones were tiny computers now, and with the internet, every single one of them contained more information than any library Steve had ever visited.

Living at the SHIELD compound, Steve dedicated a lot of his time to catching up on what he'd missed, and computers were a big help. On his third day, he came across a news item that baffled him more than any of the advanced technology he'd seen.

'Iceland announces plan for nationwide, publicly funded soulmate screening initiative,' the title said.

Steve read the article several times, but a lot of the terminology in it was completely unfamiliar to him and only served to confuse him further. After several searches and a lot of reading, it all slowly began to make sense, and yet, he still couldn't quite wrap his mind around what he'd learned.

"So, soulmates are real, then," Steve said conversationally, the next time Director Fury showed up to check up on him.

"I believe the current terminology is pincs," Fury said, his expression as difficult to interpret as always. "But yes, so it seems. A dream come true for the romantics, great business for the biotech companies, and a nightmare for those worried about privacy and an individual's rights to their genetic information."

"I always thought it was hogwash," Steve said, shaking his head and crossing his arms. Hearing it from Fury, who was no-nonsense about everything, somehow made it seem more tangible than the dozens of websites and the handful of scientific texts he'd read.

The corners of Fury's lips curled into the slightest of smiles. "Well, tell you the truth, Captain, you're not alone in that. Sometimes, it turns out we don't understand the universe quite as well as we assumed."

"Not that it makes a difference to me. If I had a soulmate, they'd be dead by now, right?" Steve had to check.

"I'm no expert, but from what I've gathered, I don't think anyone really has an answer to that," Fury said. "Maybe you could have a contemporary match. It might not be what you expect. Maybe you think it'll be a young lady, and it turns out to be an old man. I've heard of cases were people regret having found out, and would've been happier not knowing."

"It's even worse than I thought, then," Steve said, reaching for his gym bag. He had a feeling he'd do quite a few more rounds and maybe break a bag or two after this conversation. "Well, I don't think I want to know."

Fury nodded. "That's up to you, of course. If you don't, you don't. If you ever change your mind, let us sort it out for you. As you may have heard, around here, it's private companies that do the matching. We'd rather not have you putting your genetic information out there, but we're on good terms with Stark Industries. I'm sure we can arrange something."

Steve had been moving towards the door, thinking he was done with the conversation, but he stopped in his tracks to frown at Fury. "Wait, Stark Industries, as in, Howard's company?"

"The one and the same," Fury confirmed. "Howard's son Tony took over from him. I'm sure you'll be crossing paths with him sooner or later."

That was the first time Steve heard of Tony Stark. He was mildly curious, and looked him up online. Tony resembled Howard a lot, both in looks and in reputation. It seemed like he might've also inherited Howard's fascination with soulmates, since his company was now the market leader in genetic matchmaking.

The second time Steve came across Tony's name was in the briefing package Fury had put together to prepare him for the Tesseract mission. There was no mention about "amoromics" in Tony's file, just a lot of information about Iron Man, his superhero alter ego. The flashy red and gold suit of armor was, again, exactly something Steve could've envisioned Howard creating if he'd had the technology to do it.

Not much later, Iron Man made his actual entrance into Steve's life outside a museum in Stuttgart, with a flash and a bang and blaring loud music.

After they'd caught and secured Loki, the demigod who'd stolen the Tesseract, Steve and Tony faced one another properly for the first time. Standing at the back of the Quinjet, Tony took off his helmet, his big brown eyes meeting Steve's, and—there was something about him that Steve couldn't put a finger on that set him on edge, sent a shiver down his spine and made his pulse jump uncomfortably. If he'd ever felt like someone was walking over his grave, this was it.

He told himself it was just a combination of the adrenalin of the fight starting to fade and of Tony's uncanny resemblance to Howard. Looking at his face was such a strange experience because of it: there was so much of his father in there, although he actually looked older than Howard had when Steve had last seen him. It was the most palpable reminder of the time that had passed that Steve had yet come across.

The moment Tony first looked into Steve's eyes on the Quinjet, he knew his life would never be the same again.

It was an unnerving, disturbing feeling, like a hit of some drug, his mind turning a little fuzzy, his breathing slowing down on its own accord, his heart thumping forcefully beneath the arc reactor.

It was as if his body wasn't entirely his own anymore.

He'd heard enough descriptions and read enough papers that he knew what this had to be, although he didn't want to name it aloud even inside his head.

It reminded him of the time when he'd first read that damn paper back in 2008, because just like he had then, he felt like on some subconscious level, he'd been waiting for this day to come. It made him seriously want to grab a bottle right now, but that wasn't in the cards, what with them having to babysit the living embodiment of an ancient Norse god.

Him and Captain America. What were the odds.

Tony was well aware of all the horror stories, from the lawsuits by homophobes who'd gotten same-sex matches to the case where an underage girl had managed to slip her genome into a database and ended up stalked and harassed by her very much adult and all too entitled match. This had to take the cake, though.

It took him a lot of restraint not to break out in hysterical laughter.

Tony did his damnedest to hold back what he felt and to answer every single word Steve said with a quick wisecrack, simultaneously searching for any sign of a reaction on Steve's extremely handsome face. He couldn't catch one, nothing beyond exasperation and confusion, and try as he might, he couldn't tell if some of the jumble of feelings buzzing through his mind might be coming from Steve.

Steve had to be feeling all this too—as far as Tony knew, the synchronization was always reciprocal. Then again, he was pretty sure there were no precedents for matching with a super soldier who'd spent decades in accidental suspended animation. It'd be just Tony's luck to be the first example of a failed, one-sided match in the whole wide world.

The only good thing was, they had no time to stop and waffle on about feelings. Thor, another godlike Asgardian, showed up and tried to grab Loki, offering Tony the perfect target for some of the frustration and despair he'd managed to build up during the brief period of time he'd spent with Steve. Since he was fighting a superpowered alien, he didn't even need to hold back. It was pretty great.

Overall, it really helped to have other people around and other things to focus on, like the threat of an extraterrestrial invasion, or a spy organization secretly building weapons of mass destruction. For several hours after that brief moment of panic on the Quinjet, things were perfectly fine, so that Tony almost managed to convince himself he'd in fact imagined the whole thing—Steve was a handsome guy, maybe Tony had just massively, embarrassingly over-interpreted a mix of post-battle endorphins and a severe instant crush—but then he found himself standing inches away from Steve in Bruce Banner's lab on the SHIELD Helicarrier, and he felt it all again, just as strong as the first time, if not worse.

Everything was simultaneously hazy and hyperreal; the other people in the room faded into insignificant background noise, but he could count each one of Steve's long curly eyelashes and hear each angry huff of Steve's breathing, almost perfectly in time with his own. He couldn't decide whether he wanted to punch Steve or pull him into a kiss. It was disturbing and intoxicating and something he desperately craved but knew he should run away from.

The thing that finally broke through the trance was everyone else in the room freezing to stare at Bruce, who was holding Loki's scepter.

The alien scepter harnessing who knew what powers, the stone at its end glowing a mysterious blue—what if—could that be it?

Tony ran a hand over his face, feeling like a drowning man desperately reaching for a lifeline. It could explain everything. Loki had had the scepter with him all along. Maybe it had been messing with his mind from the get-go. Maybe he and Steve didn't match. Maybe it was all just magic and mind control.

He'd never thought he might some day consider "mind control" the lesser evil out of any set of options, but in this case, it really would've been. The problem was, he knew he was grasping at straws. He'd felt what he'd felt. It had been real. He was still all too aware of Steve standing next to him, and he couldn't shake that off.

A few seconds later, something exploded, and from there on out, they were in full Avenging mode again, with things blowing up and people dying and alien armies pouring out of a wormhole, and Tony was constantly too busy or too shocked to think about Steve, until he was flying into said wormhole carrying a nuke.

At the last minute, he tried to call Pepper, but she didn't pick up. He wasn't too surprised. Instead, he was relieved. He wasn't sure what he would've said, anyway. Pepper had Happy now, and they were happily matched; confessing those feelings Tony had never told her about as his last words wouldn't make anyone feel better about anything.

He also wasn't entirely surprised that she wasn't on his mind when he closed his eyes, certain he'd never open them again. It was Steve, instead, and all the pain that this would save him.

It was best for everyone this way.

None of the death and destruction he'd witnessed or any of the hits he'd taken during the long and terrible day had hurt Steve as much as it did to see Iron Man fly into that wormhole. It was a one-way trip, and they all knew it. He waited until the very last minute, holding on to hope that Tony would somehow make it back anyway, but in the end, he had to accept the grim reality. He told Black Widow to close the portal.

The wormhole started to shrink, the unnatural gap into some alien void sealing itself, but just before it vanished entirely, Steve could see a tiny shape emerging through it. A human figure, hurtling towards the ground. Iron Man.

For a brief moment, he was overjoyed, only to have that turn into a cold fear clawing at his gut when Tony didn't slow down. He wasn't flying, he was falling.

Hulk caught him in mid-air and deposited him on the ground, and Thor wrenched off his faceplate to reveal Tony's pale and lifeless face.

"Is he breathing?" Steve called out as he hurried to crouch over Tony's armored form.

Holding his ear over Tony's mouth and nose gave him his answer, and it was exactly the one he'd feared: he didn't feel or hear the slightest whisper of air. The blue light in the chest of Tony's armor had gone out. Steve had read his file, and he knew Tony needed that to live.

Tony hadn't really returned from that wormhole after all.

Steve had known Tony for less than a day, but the man had gotten under his skin in a way he couldn't have expected. Tony was loud and annoying and confrontational, but he was also bright and funny and charismatic, and he seemed to fill a room the second he walked into it, instantly catching everyone's full attention. The thought that he was gone hit Steve hard. It felt as if something were missing, something he'd not even realized was there, like a background noise just at the threshold of his hearing that had been silenced. The world felt terribly empty and lonely without it.

Hulk roared, a bone-shaking rumble loud enough to wake the dead. It didn't wake Tony.

Steve had to do something, even though he knew it was probably too late by now. He took a deep gulp of air and bowed closer to Tony again, pinching Tony's nostrils closed and pressing his lips against Tony's, trying to breathe life back into his still lungs.

The moment their mouths touched, Tony flinched and his eyes flew open. Startled, Steve jumped back, falling onto his haunches.

"Did you just kiss me?" Tony asked, voice raspy, eyes wide, his mouth hanging open after he'd stopped speaking.

Steve grinned back at him, the joy and relief at seeing him awake and alive so overwhelming, they left him feeling as breathless as Tony sounded.

"It wasn't a kiss," he said quickly.

"Okay, then," Tony said, still looking dazed. "So, did we win?"

The truth was, Steve wasn't entirely sure what that had been and what, exactly, had happened. Even though he'd never admit it, deep down, he kind of wished it had been a kiss. The thought came with an instant wave of guilt; he was sure Tony wouldn't have wanted that. It was wrong. He might be incredibly confused about his feelings for Tony, but he'd gotten a pretty strong impression that Tony couldn't stand being around him.

5. Spatial and Temporal Limits of Synchronization in Persons with Identical Non-Coding Sequences. 2012.

All early studies had high error margins due to the lack of means to definitively identify PINCS. Our results from a carefully selected set of test subjects confirm and reinforce many previous hypotheses. It's well established that both the physical synchronization and the psychological responses depend on proximity, with skin-to-skin contact providing the most robust effects, and their intensity diminishing with growing distance [3,5]. In our study, we show that the synchronization becomes undetectable at a widely varying range (50 ± 35 m). This range is independent of the couple's awareness of one another's locations, unaffected by the absence of any visual or auditory cues. These results seem in line with the prevailing hypothesis that the synchronization effects are partially mediated by a volatile signalling molecule, such as a pheromone [6-8,11].

"Are you sure you're all right?" Pepper asked, her voice cautious.

Tony was resting on his back on a couch, on a residential floor of the Tower that had survived the narrowly missed Lokicalypse unscathed, unlike most of the neighborhood. He'd swapped his glitchy arc reactor for an intact one and had Jarvis run some basic medical scans, and everything checked out. Physically, he was surprisingly okay.

"I'm pretty sure I'm not all right," he told Pepper, "but it's not something that can be fixed."

With his arm flung over his face, he could see a vast expanse of space, stars blocked by the alien army in front of him, monstrous machine-beasts and spacecraft too large to comprehend, an assault force that could take over Earth in a matter of hours. He shuddered and pressed the heels of his hands against his eyes instead. The vision shifted, the colorful blotches behind his closed eyelids coalescing into a radiantly smiling face, handsome, blonde and blue-eyed—and almost as intimidating as those aliens.

He heard Pepper's heels click against the floor as she approached him. "Tony," she said, a question and an accusation in one word.

"Steve Rogers," Tony said, staring at the ceiling, willing the monotonous gray of it to fill his mind and wipe away those images that kept haunting him.

"Captain America? What about him?" Pepper asked, right next to Tony now.

Tony swallowed, but that did nothing to the lump at his throat. "I think we're a match," he blurted out.

It seemed to take a few seconds for Pepper to catch what he meant, but then, she said, "You and him? Tony, that's amazing!"

Tony finally turned his eyes towards her, to see that there was a smile playing on her lips. Tony scowled at her. How could she not see this for what it was?

"It's a disaster," Tony said. "There's no happy ending for this story. There's just a thousand different ways it can go horribly wrong."

Pepper sat down by his side—the sofa was wide enough to fit them both comfortably—and placed a hand on his arm. "Believe me, I know it can be a big surprise and a shock at first. I really didn't expect to match with Happy. Honestly, I thought it'd be someone I don't know at all. Not that I knew him well. I'd mostly just seen glimpses of him, and never spent enough time with him to suspect anything. It wasn't some storybook love-at-first sight scenario. It took time for me to get used to the idea. Now that I am, though, it's like he's always been by my side, and I can't imagine my life without him." She sounded all compassionate and not the least bit condescending, and Tony felt guilty that it still grated on his nerves when he knew she was genuinely just trying to help.

He backed away on the couch, sitting up and crossing his arms so that she had to let go. "Save me the sales pitch, Pep." He was being unfairly rude. He couldn't help it. "I've been in the business long enough. I know all the clichés. It's not going to be like that between me and Steve. I'm not even sure he feels it. If he does, or if he ever finds out, he sure as hell isn't going to be okay with it."

The memory of Steve's smiling face above Tony's took over his thoughts again. The smile quickly shifted to a thoughtful look, like it had, and with that came the wave of regret which Tony had felt but which definitely hadn't been his own. The very idea, the joke that Steve might've kissed him, had filled Steve's mind with nothing but remorse.

Pepper was frowning at him. "If you're matched, he'll feel it, too," she said. "You should test it so you'd know for sure. Maybe this is something else. There are theories about partial matches and synchronization that's not DNA-based and other things like that."

"It's not something else. I felt it, Pepper." Tony tapped at the arc reactor. "There's no other explanation, no matter how much I'd like to have one. Which is exactly why I'm not going to get it tested. You know I couldn't do that without his consent, which would mean talking to him about it. Nope. No way."

The law was clear on this: if a match was found, both parties had to be told about it. It was for everyone's protection. Handing over your genome to a database meant you agreed to that. Tony could easily go outside the books, of course—he could probably get hold of Steve's DNA without his knowledge, run the sequencing and alignment just for the two of them if he wanted to, but that'd be both illegal and so deeply unethical he wasn't going to consider it. He could only run the test if Steve also wanted it. If Steve agreed to it, he'd have the right to know the result.

"If you ask me, you'd still be better off knowing for sure," Pepper insisted. "If it turns out you're wrong, you'll save yourself a lot of grief. If you're right, well, you can't know for sure how he'll take it. You might be surprised. Besides, having a match doesn't mean you have to do anything about it. Plenty of pincs never get romantically involved and become good friends instead. Some decide they're too different and not right for one another and go on with their lives."

Tony let out a rueful chuckle. If it were that easy, he wouldn't have a problem, would he? "Yeah. Neither of which is really an option. You've not met him. He's…" He ran his hands over his face, searching in vain for words that didn't sound like platitudes, but his wit was failing him. "I get it now why dad always talked about him. He's one of a kind."

Pepper was quiet for a beat, and when Tony glanced at her, the look she gave him was shrewd. "It's not really about matching, then, is it? Being a match with someone doesn't make you fall in love, you know. That's not how it works."

"Did I say I was?" Tony complained, although he knew he might as well have. The conversation was starting to get beyond what he could handle. He stood up, feeling shaky and nauseous. There was a deep ache beneath the arc reactor that he knew no painkillers would touch, because there wasn't really anything wrong with him, even though everything was wrong. "God, I need a drink. Or ten."

Pepper got up from the couch as well, her eyes still on him. "So, that's your solution? You're just going to ignore this and drown it in liquor?"

Sometimes, it amused him in a bittersweet way how much he and Pepper were like the proverbial old married couple, even though they'd never ended up together.

"Until I come up with something better," Tony said, and headed for the elevator on slightly wobbly legs. The penthouse bar was mostly intact. It'd be poetic, sitting in the middle of the rubble with a bottle in hand, thinking about how that battle had ruined his life in more ways than one.

"You should at least talk to him, Tony," Pepper called out after him.

"I'm sure I will," Tony said. "Just not about this."

Over the days following the battle, Steve found himself thinking about Tony a lot. He met Tony a few times, too, in debriefing sessions with SHIELD, and doing cleanup with the Avengers, like when they sent Thor and Loki back to Asgard with the Tesseract.

When he wasn't around Tony, he kept thinking he'd like to be, but when they were in the same place, he felt oddly restless and anxious, like he couldn't wait to get away—even if he simultaneously wanted to be there. It would've been difficult to explain to someone else. It was as if there were two layers to his feelings, separate but merging together into one confusing tangle, so that he couldn't tell where one ended and the other began. On top of that, Steve got the impression that Tony was actively avoiding any situation where it'd just be the two of them alone. He wondered if anyone else noticed it. On the surface, Tony was his regular self, after all, charming and abrasive at the same time.

Tony offered all the Avengers a place to stay at his Tower. Bruce was the only one who took up on it right away. Clint and Natasha already had their living arrangements with SHIELD, and Thor wasn't on Earth right now.

Steve felt slightly envious of Bruce whenever he saw him and Tony together; they were usually chatting away about some advanced science or engineering topic that Steve couldn't hope to comprehend, and they seemed perfectly at ease with one another. He would've liked to have that, too.

Steve thought long and hard about moving to the Tower. It was a tempting offer. It would be nice to have people around him who had at least some idea of what he'd been through. Then again, considering how Tony was behaving towards him, he suspected Tony didn't really want him there, and had only included Steve in the blanket invitation because it would've been odd to exclude one person. He didn't know what it was that he'd done to offend Tony, but he didn't want to make Tony more uncomfortable. Living in the same building with him could get really awkward.

The solution to the situation came from Fury, who had an alternative offer: Steve could keep working for SHIELD, and they'd arrange a proper apartment for him, instead of the quarters he'd had so far. The only catch was that he'd be stationed in Washington D.C.

The more Steve considered this, the more it seemed like a good fit. The change in location wasn't really a downside. New York was too familiar. It felt like he couldn't really move on with his life with so many reminders of the past all around him. He'd also be out of Tony's hair. That wasn't really what he wanted—he would've liked to spend more time with Tony, learn to know him and figure out what was going on between them—but it was obvious Tony didn't want that.

He felt like he owed it to Tony to tell him of this decision as soon as possible. Since Tony would probably come up with some excuse if Steve suggested an actual meeting, he called Tony instead.

It took a while for Tony to pick up. It occurred to Steve that Tony was probably so busy running his company and working on his countless engineering projects that he might not have time for random phone calls. Steve was considering if he should just send an email instead or wait and call again later when Tony finally answered.

"What's up, Cap?" Tony greeted him.

"Hi, Tony," Steve said, as casually as he could. "I just thought I'd let you know, Fury offered me a job in D.C., and I'm going to take him up on it. So, I'm grateful you asked me to come stay in the Tower, but I'll have to say no."

There was a brief pause before Tony replied, "I was expecting as much. Big ugly building, not at all your style. I'm glad you've got your career plan all sorted out."

"It doesn't mean I'm leaving the team. I'll still be an Avenger," Steve added, so he wouldn't give the wrong impression. "I'd just like to have a day job, too, same as the rest of you."

"Yeah, of course. See you on the next mission," Tony said, sounding distracted, and hung up abruptly.

Steve stared at the phone in his hand, with the nagging feeling that there had been something wrong about the whole conversation. It took him a while to realize what it was.

He'd not talked to Tony on the phone before. Now that he had, it'd felt like something was missing. Tony's voice had been perfectly audible, the connection flawlessly clear, and yet, it had been as if there was usually more depth to his voice, something Steve had grown used to during face-to-face conversations that had been lacking. Something beyond the lack of his vivid facial expressions and gestures.

Overall, he hadn't felt like he usually did when he was around Tony. The more he focused on it, the more conspicuous it was that he'd only felt regret that he was saying no to Tony's offer and sadness about missing out on spending more time with his fellow Avengers. That inexplicable, anxious urge to get out of the situation hadn't been there at all.

Only one layer of feelings, not two.

Suddenly, like the final piece of a puzzle falling into place, Steve realized what might be going on. He dropped the phone on the nightstand with a clatter and sat down on his bed so heavily, both the springs and the floor creaked in protest.

Whenever he'd been actually, physically in the same place with Tony and talking to him, properly focusing on the conversation, he'd often had this hard to pin down sensation of something being a little off, not just in his head but physically, almost like he was coming down with something. He called to mind what he'd read about how people felt when they were around their soulmates. Lightheadedness, shortness of breath, palpitations, disorientation, dissociation, sudden mood swings—he could tick off every single thing he could remember. He hadn't felt all of that at once, of course, but one time or the other, so that there was definitely a pattern there.

Maybe the explanation for all his perplexing feelings was that they weren't really his at all, but Tony's. It could even explain why Tony was behaving like he was. If he'd already figured this out and didn't want it, of course he'd be in a hurry to get away from Steve.

It all fit together and made sense when he thought about it.

He'd never wanted a soulmate, but if he had to match with someone, Tony was as good as he could hope for: someone he genuinely appreciated and found intriguing. Easy on the eyes, too. Steve had never thought he might end up in a relationship with a man, and he knew that even if they were soulmates, that didn't mean they would. If they did, though—surprisingly enough, he wasn't entirely opposed to the idea. Sure, it also felt a little unnerving, but as much as he was a man of the past, Steve had never been afraid of the new and the unexplored.

If he was right about this, maybe he could talk to Tony and convince him this was something worth looking into.

If it turned out to be true, he might reconsider his plans not to move to the Tower.

He picked up the phone again to call Fury, but he wasn't going to say he'd accept the job. He was going to ask about taking that soulmate matching test, so he could know for sure.

6. First Two Years of Longitudinal Investigation of the Los Angeles Cohort of Persons with Identical Non-Coding Sequences (LILAC-PINCS): Summary of Findings and Future Prospects. 2014.

There is some anecdotal evidence for side-effects caused by lack of contact with a synchronized partner⁵, but our results consistently contradict this. While the negative mental health effects for persons who strongly desire a match and fail to find one are undisputed^31-33, the matched couples in our cohort seem to fare no better nor worse than control couples who are not PINCS. The lower incidence of breakups and divorces among PINCS compared to non-match couples can be seen as a positive outcome, but this difference is not statistically significant; a longer follow-up period is needed to confirm whether this is an actual effect or merely coincidental. We find no support for the claims that some PINCS experience one another's injuries or illnesses^2,5; on the contrary, we show that a strong enough negative stimulus, either mental or physical, will temporarily override the synchronization in most cases. This makes sense as a protective mechanism, as it leaves the unaffected partner capable of assisting the one in distress.

"So, on the plus side, the armor upgrade is awesome." Tony rubbed at the micro-repeater implant on one forearm. Unlike the arc reactor, which was a constant background ache even on a good day, he could barely feel the chips that allowed him to link with Mark 42. "On the downside," he went on, "a lot of good people paid a high price for me being an asshole. Overall? A spectacular clusterfuck, even by my standards."

He sat up on the divan to reach for the cup of coffee on the table, only to find out it had gone cold. He drank it anyway, wishing it were something stronger. Unfortunately, Bruce's lab didn't come with a bar. He should fix that. In case of emergencies. Which he always seemed to be having plenty of.

Bruce straightened up in his seat, taking his glasses off and rubbing at his eyes.

Tony squinted at him suspiciously. "Don't tell me you slept through all of that."

"No, no! Some of it? Maybe?" Bruce said sheepishly as he put his glasses on his nose again. "But, you know, it wasn't your fault. You may be an asshole, but none of what happened was your fault."

"Maybe not, and yet." Tony sighed, turning the empty mug around in his hands. It was completely unfair that he'd made it through the whole mess with nothing worse than bruises. "Maya's dead, Happy's still in the hospital, and Pepper's not a fan of her newly acquired superpowers."

Bruce's lips curled in a rueful smile. "Now, there's a feeling I'm all too familiar with. Luckily, in her case, it might be reversible."

"It had better be," Tony said. He'd already sent her samples to his top geneticists. There were certain advantages to having a strong presence in the biotech field. "Honestly, she's put up with so much crap from me, she should be nominated for sainthood. It's a proper miracle she hasn't walked away ages ago."

"Just guessing here, but, you know, maybe she sticks around because she actually likes you," Bruce suggested.

"She likes Happy," Tony corrected him. "She tolerates me. On most days."

Bruce eyed him skeptically. "I may not be the most perceptive guy there is, but surely it's more than that. She cares for you, just like you do for her."

"And she's happily matched with Happy." As soon as the words were out, Tony realized they'd probably sounded bitter, even though he hadn't meant it that way. Really, it was best for everyone.

He was absolutely certain that if he'd ended up together with Pepper, matching be damned, she would've been miserable most of the time. Especially considering what a wreck Tony had been for the past few years. Not that he hadn't been a wreck before that. No, he'd just metamorphosed from a partying, drinking, selfish asshole of a wreck into one with good intentions that often ended up causing property damage and mental and physical trauma to himself and the people around him.

"Seriously, Tony?" Bruce said, even more incredulous. "That's what you're going with? You're the last person I'd expect that kind of genetic determinism from. You think matched relationships are automatically more meaningful than non-matched ones, then?" Bruce eyed Tony over the rims of his glasses so that for a moment, he resembled a stereotypical shrink, as much as he actually wasn't one.

"I don't!" Tony exclaimed, holding up his hands, palms out. "Matching might be good for business, but if I could decide, I'd rather just forget that there are those stupid chunks of junk DNA in our genomes."

"What's stopping you? Even if you're professionally involved in that, it doesn't have to figure into your private life," Bruce said. "It's not like it's mandatory to have your sample in an amoromics database."

"It isn't," Tony said.

Bruce blinked at him. "I know, that's what I just said?"

"I meant, my genome's not in the database," Tony clarified.

"Huh. There's another surprise," Bruce said. "I thought yours would've been among the first StarkAmor entries, that thing even has your name on it. I bet a number of people sent in samples just because they hoped to match with you."

"Eurgh." Tony shuddered and pulled a face. "For the record, I hate that name. With a fiery passion. That, and pretty much everything else that has to do with amoromics."

"Then I really don't get what the problem is. Just look at the Avengers. It's not like any of us are actively looking for a match." Bruce held out a hand, ticking off fingers as he went on: "Natasha and Clint are probably too neurotic about their privacy to hand over samples to anyone. Steve's genome is classified, for sure. Thor isn't even human. And me, well, I've got a big green reason not to, and even if I wanted to, after the amount of mutations the gamma exposure left me with, it'd probably be a pointless exercise."

"If you must know, the problem is that I've actually met my match, and I wish I hadn't," Tony said. It came out as off-hand and distracted instead of the dramatic revelation it could've been, because he had the nagging, tip-of-the-tongue feeling of an idea that was starting to take shape.

He had all this gene technology at his use, with some of the world's best minds on his payroll—Stark Industries' biotech division had grown way past being a glorified high-tech dating service. They were involved in plenty of medical genetics research. Diagnostics and therapeutics. They were good enough at it that they'd probably be able to rid Pepper of Extremis.

Bruce thought the gamma radiation could've messed up his INCS. If that could happen accidentally, then surely it could also be done on purpose.

Bruce had been talking to him for the past half a minute, but Tony hadn't heard a word of it. He stood up and started to pace, too excited by his eureka-moment to stay still. Bruce fell quiet, peering at him curiously.

"Identical Non-Coding Sequences are a genetic anomaly, right?" Tony began. "Well, we've got the science to fix that sort of thing." He spread his arms showily, as if he were speaking to a much bigger audience.

Bruce's eyes went wide, and Tony thought there might've been the slightest flash of green in there. "Oh, no. No. Tony, that's a terrible idea," he said hurriedly. "We haven't even figured out the molecular pathways behind the synchronization phenotype. There's no way to know what kind of side-effects tampering with those sequences would have. Besides, you wouldn't know which tissues to target. You might need to deliver your hypothetical gene therapy to every single cell."

"Uh uh. As it happens, Maya Hansen and Aldrich Killian already came up with the perfect nanotech vector to do just that," Tony said.

That only made Bruce look more upset. "It also has the side effect of making people spontaneously combust! I don't know who this mysterious match of yours is, but they're not worth killing yourself over."

"Aww, no need to worry for me, Green Genes. Relax. I'm not going to. It's just a thought experiment," Tony said.

He meant it, too. A tiny part of him still held onto the hope that somehow, he and Steve could work things out and end up as something more than teammates. Until he managed to extinguish that, he wasn't going to do anything extreme. Besides, it wasn't like he could whip up something like that overnight on his own. Even though he was an engineering genius, he was no genetic engineer. He wouldn't even know where to start.

He was going to look into it, though.

Just the idea of a possible way out felt great. Instead of having to indefinitely grit his teeth and passively suffer this situation he'd never wanted to be in, he'd just come up with the beginnings of an escape plan.

"It was not my first kiss since 1945. I'm ninety-five, not dead," Steve told Natasha, letting his eyes leave the road ahead for long enough to give her a sideways glance.

It was a lie, of course, and she could probably see right through it. He'd been on a few dates. They hadn't felt quite right. He wasn't the kind of guy to kiss on a first date, anyway. That kiss with Natasha had been just a ploy to distract pursuers, and he tried to take it as such. The memory of it still made him feel awkward. It'd been so sudden and surprising, and even though it'd felt wrong, he couldn't deny it'd also been kind of nice to share that kind of intimacy with someone, as brief and meaningless as it might've been.

"No one special, then?" she pressed on.

"No," he replied.

Of course, his mind instantly went to Tony.

He'd thought Tony had died, not long ago. The memory of seeing the news, the image of Tony's Malibu mansion as a smoking ruin, was still fresh: how he'd tried to feel something about it, prodded at the idea of Tony being gone like testing an injury to see how bad it was. All he'd gotten was numbness and disbelief. It hadn't felt real. When it'd turned out Tony was, in fact, alive and fine, the relief had been equally underwhelming. He'd not seen Tony since. Considering that Steve was now a fugitive from his own employer, he wasn't expecting to, either, not anytime soon.

"I've got a question for you, too, if you don't mind," Steve said.

"Shoot," Natasha said. "I promise I'll answer. It might even be true."

Steve was pretty sure he knew what the answer would be. "Have you done that soulmate gene test?"

"Me?" Natasha chuckled aloud, clearly taken by surprise. "Do you really need to ask? I have dozens of reasons not to. Have you, then? Or thinking about doing it?"

"I have," Steve confessed. "There wasn't anyone."

He'd even let himself get a little excited about it. He'd thought it'd confirm what he'd already guessed. Instead, he'd gotten the opposite: an impersonal form letter telling him that at this time, no one in the database matched him. It'd come with a disclaimer that like all genetic tests, this wasn't foolproof, and also that the negative result didn't mean there was no one out there for him, just that their data wasn't currently available.

It was Tony's database. Tony's data wouldn't be unavailable.

Steve had concluded that his first earliest hunch had probably been true, and any soulmate he might've had was either dead or very old by now. He didn't expect a lot of nonagenarians to have sent their samples for soulmate matching.

Whatever he'd thought might be going on between him and Tony, that must've all been in his head. They weren't soulmates.

They were barely even friends.

He wished things could've been different.

He wondered how long it'd take for him to stop thinking about Tony.

"I'm sorry to hear that, Steve." Natasha placed her hand on his shoulder and gave it a light squeeze.

Steve replied with a little smile that he wasn't really feeling. "Thanks, but it's okay. It's probably for the best. Just look at us. The lives we lead aren't exactly cut out for stable long-term relationships."

"Maybe so, but that doesn't have to mean we should stop trying," Natasha said.

"I'm not going to," Steve said.

He wasn't sure whether he really meant that or not.

7. Synchronization in Persons with Near-Identical Non-Coding Sequences: Implications for the Molecular Basis of the Synchronization Phenotype. 2015.

The subjects were a subset of the 986 person cohort recruited for a previous study (14) who had, at the time, consented to the use of their genomic data for further research. We used a cutoff of BLAM (15) score between 95 and 98 to define pairs of individuals who share near-identical non-coding sequences. Out of the 34 pairs of subjects with sequences in this range, 14 agreed to participate. The study was performed in accordance of the Declaration of Helsinki as well as the PINCS Privacy Guidelines, and all subjects gave informed consent. Physiological effects were measured using the Standardized Synchronization Scale for PINCS (SSSP, 16), and the psychological effects evaluated with the 30 item Mental Matching Questionnaire (MMQ30, 17).

Steve took in the room in front of him. It was the smaller of the Bartons' guest rooms; the larger one had been offered to Natasha and Bruce by unanimous decision. Thor had headed off on some mysterious quest of his own, so he had no need for a bedroom. This particular room that'd been designated to Steve and Tony only had one bed, and it seemed narrower than a standard double. Since Steve was kind of wider than standard himself, that would make it a snug fit.

Tony stepped into the room half a minute after Steve, and the feeling of Oh, fuck, no that followed was so tangible, Steve could've sworn Tony had spoken those exact words aloud, even though his lips hadn't moved.

"It's just for tonight, we can manage," Steve said. He was used to cramped sleeping arrangements—during the war, they'd been the norm more than the exception.

"Thanks, but I think the floor looks extremely inviting," Tony returned curtly. The look on his face was mildly hostile, in line with his voice, and yet, somehow, Steve was sure Tony was more anxious than angry. So sure, he felt his own heart beat faster in response.

It was as it'd always been when he was around Tony. He'd expected that to stop when he'd found out they weren't soulmates; he'd thought it'd rid him of these apparently imaginary impressions that he kept having, but it hadn't. The best explanation he'd come up with was that maybe he'd known Howard so well, he could now notice slight changes in Tony's voice and barely perceptible microexpressions on his face so that he could pick up cues he'd miss in anyone else.

Of course, he didn't even know if these inklings he had of Tony's moods were correct. It wasn't as if Tony was going to admit that he was, for whatever reason, currently as nervous as he might've been standing next to Ultron.

"Okay, if we don't want to share, you can take the bed," Steve offered.

Tony glared at him. "You think I'm too pampered to handle one night on the floor, Rogers? I'll have you know, I've slept on all kinds of hard surfaces plenty of times. Sure, most of those involved booze, but still. Nothing new." He walked over to the bed, grabbed a pillow and a blanket, and dropped them on the rug. "There, I'm all set."

"Fine," Steve said. He had no need to turn this into an argument. Instead, he headed out of the room to see if the bathroom was free.

Once he got back, Tony was on the floor, under the blanket, his back towards the door and the bed. He wasn't asleep, though, but propped up on one elbow, the glow of his cell phone screen giving his face a sickly bluish cast. He didn't turn to look when Steve entered. Even without any mysterious intuition, it was obvious he didn't want to talk.

"I guess you won't need light?" Steve asked.

"Nope," Tony replied, his eyes still on the phone.

Steve switched off the lights, walked over to the bed, and settled under his blanket.

Sleep took some time to come, both because the day had left his mind reeling, and because of the lingering anxiety that might or might not be radiating from Tony. Maybe it was all Steve's.

He'd come so close to actually sleeping in the same bed with Tony. A part of him, the part that had readily latched on to the idea that they could be soulmates, would've liked that very much.

Eventually, he did drift off, only to wake up to the sound of creaking floorboards. He sat up, looking around, ready to leap into action, but it was only Tony, halfway to the door, his silhouette just visible in the sliver of pale moonlight escaping the curtains.

"Can't sleep?" Steve called out.

Tony stopped in his tracks. "Yeah, surprisingly, turns out knowing that I'm responsible for a murderbot that threatens to take over the world isn't a cure for insomnia." Steve couldn't make out his face in the dim light, but he could picture the expression easily enough, going by the sardonic tone.

"You didn't mean for that to happen," Steve pointed out. He did think Tony had been reckless and meddled in something he didn't really understand, but he didn't blame Tony, not really.

"Tell that to all the people who've gotten hurt because of it," Tony said.

"We're going to sort this out," Steve said, trying to sound as encouraging as he could, hoping his confidence could somehow counter the despair he heard in Tony's voice. "We're all in this together. We can do it."

"Thanks, but your pep talk is going to be totally wasted on me," Tony scoffed.

Although he sounded even more annoyed than he had to begin with, the despair Steve had caught earlier took a new undertone of longing and sadness, so deep that it stole his breath away and brought tears to his eyes.

"Tony—what's going on between us?" Steve blurted out. He hadn't meant to say it, not really, but in the intimate setting of the dark bedroom, it didn't even feel out of place. "I know I can be stubborn and I've been called self-righteous, may even have deserved that," he went on, "but honestly, I can't figure out what it is I've done to you that you can barely stay in the same room with me for two minutes."

"Wait, how is this now about us?" Tony asked.

Now that Steve had started, he might as well keep going. "It's about us because we're teammates, and I'd like for us to be friends."

"I think that ship sailed a long time ago. Vanished past the horizon. Probably sank as well," Tony said, his voice harsh. The contradiction between that and what Steve thought Tony felt still remained, the regret lingering in the spaces between his words and in the shaky breath he drew afterwards.

"It's not too late. We're here, now." Subconsciously, Steve reached a hand towards him, though Tony might not even notice it in the dark.

"Some doors are better left unopened. Or should that be ships, unboarded?" Tony joked. It wasn't funny.

"Sometimes, you just step on that gangway on the wrong foot, and that's a mistake that can be fixed," Steve tried.

"Ouch, I think that's enough mangled idioms for one conversation. I'm heading to the quinjet. Going to try to get some work done," Tony said, the floor creaking as he took a step towards the door.

"You should leave that for later and try to rest. Tomorrow's going to be another long day," Steve said, even though he knew it was pointless.

"Well, if Mr. Sandman catches up with me, I can take a nap there just as well. Good night, Steve." Tony opened the door to enter the equally dark hallway beyond.

Somehow, it seemed to Steve like he was walking away from more than just one conversation, or a shared bed in a guest room.

"Good night, Tony," Steve said.

Tony was struggling with two addictions in his life.

The first and oldest, of course, was booze. He didn't think he had a problem, not really, but Jarvis had started nagging at him, citing that the added cardiovascular risks from drinking didn't play well together with the added cardiovascular risks from the arc reactor still lodged in his sternum. He couldn't really argue against that. Then again, he also didn't care very much. If he ended up living a few years less than he otherwise would've, what did it matter?

Jarvis was gone, now, anyway. Jarvis, who'd had no physical body that could fail and should've easily outlived Tony. The Vision was something else, something that Tony didn't fully understand. Friday, well, she was as good as any AI he'd ever coded and he liked her and was proud of her, but she wasn't Jarvis, and never would be.

So, yeah, Tony probably drank more than was good for him. Sometimes, he tried to cut back on it. It usually didn't last very long. That often had to do with his second addiction.

Being around Steve was a lot easier when he was in armor, so he tried to stick to that whenever he could. Scientists still hadn't managed to figure out how the effects between PINCS worked, and although the crackpots were name-dropping anything from quantum entanglement to gut microbes, the prevailing consensus among respectable biologists was that it involved some difficult to detect airborne molecules. Apparently, even if they were undetectable, the suit's air filtration managed to get rid of them for him. Being in a room with Steve as Iron Man, Tony could convince himself he'd gotten over it and moved on with his life.

The problem was, even three years after they'd first met, being in a room with Steve while not in the suit was every bit as intoxicating as it had been to begin with. It was one of the reasons people cited for why matched relationships tended to last longer than non-matched ones: those new relationship feelings of infatuation could persist for years. Possibly also the reason why unrequited crushes on matches could last forever—except that by now, Tony had finally managed to convince himself that whatever was between him and Steve, it couldn't be a regular match like most PINCS had.

That night at the Bartons' had been a revelation. The way Steve had acted all confused about Tony and their non-relationship, he might've as well spelled out in big fiery letters that he had no idea they were a match. Had he been feeling even half of all this stuff Tony was struggling with, he must've at least suspected something, so really, this could only mean that they actually weren't a proper match, and it was, somehow, one-sided.

Partial matches were a known thing: there were a handful of scientific articles concerning people whose genetic markers weren't identical, but close, with just a few mismatched nucleotides here and there. Occasionally, this could lead to a milder version of the synchronization phenotype. Sometimes, it was asymmetrical. Maybe that was the explanation.

Of course, there would've been an easy way to find out. All he'd need to do would be to ask Steve, run the matching algorithm on their genomes, and he'd know.

He just didn't want to.

It was easier to keep his distance and do his best to ignore the whole thing. It'd be particularly easy now that Ultron was dealt with, there was a fresh crop of Avengers for Steve to train, and Tony could take an indefinite leave of absence from the team.

Saying goodbye to Thor and Steve outside the shiny new Avengers complex, he felt more relieved than anything else, even if it was mixed with some nostalgia from Steve. That had to be all Steve's. Tony wasn't nostalgic.

He still put his sunglasses on to block some of his expression, just out of habit.

"It won't be the same without him. Or without you," Steve said, as earnest as only Captain America could be. There was a small smile playing on his lips as he eyed the intricate, vaguely Norse-looking pattern Thor had left on the lawn.

"Of course it won't. I'm going to miss him. And you're going to miss me. There will be lots of manful tears." Tony kept his voice breezy and casual. He was very good at that; he could do it even though Steve's words had stung like he'd just stabbed Tony in the gut.

Steve frowned at him, suddenly all serious. "I will miss you, Tony."

"I'm sure you'll get over it," Tony said, and started walking towards his car. Steve followed.

Maybe he'd finally get over it himself, too, with this realization that he might've been wrong from the start, and that they might not a proper match, after all.

"I think I've done enough damage for now," Tony went on. "Better go and lie low for a bit. Maybe I should get a secret hideout like Barton's. Just minus the kids and the matched spouse."

"Ruled those out, then?" Steve asked, his tone light but his expression still thoughtful.

That could be interpreted in a couple of different ways, but really, Steve was practically asking Tony if he'd looked for a match. He could've laughed. If he'd needed further proof Steve didn't suspect a thing about the two of them, it was right there.

“Technically, it's impossible to prove that you don't have a match,” Tony replied; a scientifically accurate answer that handily exempted him from having to say anything more.

Steve's lips quirked into something that wasn't quite a smile, and the nostalgic feelings Tony got from him seemed to catch a different timbre. "Things used to be so much simpler before the ice. I never believed in soulmates back then. Never wanted one. I did think I'd like to have a family, though," Steve said wistfully. "Now? I don't know."

Tony did laugh at that, a dry chuckle that wasn't really amused, like Steve's smile hadn't been a smile. "That makes two of us."

He didn't know what he wanted anymore. He hadn't wanted a soulmate. He had wanted Steve. If Steve wasn't his exact match, there might be someone else out there who was. Tony felt sorry for the poor bastard. He wasn't about to go looking for them.

As for family—he didn't think he'd be any good with kids. His dad had been terrible, and he doubted he'd do any better. Still, he would've liked to have a family. A group of people around him that looked after one another. He'd thought the Avengers could be one. For a brief, happy period of time, they almost had been. Almost, but not quite, mostly because he'd always kept that distance between him and Steve. And now he was about to drive away from it.

He sniffed. Definitely not close to tears.

He was glad he was wearing the sunglasses.

Thankfully, at this point, he was standing by his ride and had an obvious escape route. He opened the door and slipped behind the wheel.

"You'll pay us a visit every now and then, right?" Steve asked hopefully.

"Maybe," Tony said. ”Look after the kids for me.”

He waved at Steve and closed the door.

8. An Improved Search Algorithm for Paired Identical Non-Coding Sequences. 2016.

The bottleneck for amoromics analyses has always been the bioinformatic step; the problem of finding randomly located identical sequences shared between two genomes is far from trivial. Several strategies are commonly used to make these computationally intensive analyses more feasible. Most amoromics pipelines focus on chromosome 21, and include tools for masking protein-coding regions and common repeat sequences. However, nearly all analysis software, whether commercial or open-source, still rely on the original BLAM algorithm from 2009 to perform the actual database search. Here, we present BLAMMO, an improved algorithm that retains the accuracy of the original one, but performs up to 60% faster.

If Tony had thought his life had been a mess before, that'd been nothing. That'd been like a paper cut compared to a fatal wound, or a first world problem compared to a global disaster.

Damn, but wallowing made him poetic.

He realized the bottle was empty, and annoyingly, had to get up to fetch another one. He was a little dizzy, but not so much it'd slow him down. Clearly could do with a few more drinks.

He grabbed the first bottle that happened to be on the shelf, not bothering to look at the label. It was his bar. Only nice things in it. The really expensive stuff was stashed away on the higher shelves so he wouldn't waste it while on a binge.

He flopped back onto the couch, staring ahead but not really seeing the room around him.

He'd already thought he'd lost the Avengers a year ago, when he'd taken a step back. He'd thought he'd let go of Steve. He hadn't, not really, not back then. Now, he really had.

Most of the team would've still be in prison if Steve hadn't broken them out. Now they were on the run, who knew where, and they all hated Tony's guts.

He kept telling himself he'd done his best in what had been an utterly fucked-up situation, but he didn't really believe it. He should've done better. If he'd gotten through to Steve so that Steve would've accepted that olive branch, he could've prevented most of this.

Steve.

Steve had known Barnes had killed Tony's parents, and he'd never said a word, but then, why would he?

"He's my friend," Steve had said, facing Tony's armored form without fear or hesitation. Not an apology, but an explanation.

And I never was, Tony had thought. All he'd said had been, "That's no excuse."

They had been teammates. They hadn't been friends. Tony could really only blame himself for that, too. He'd been too afraid of whatever quirk of genetics had connected the two of them. Maybe if he hadn't been, things would've been different. Maybe Steve would've told him about Barnes before it was too late. Maybe he would've signed the Accords.

The stupidest thing was, Tony thought, as he took a swig of the bottle—rum, wouldn't have been his first choice if he'd actually been looking, but eh—he still couldn't bring himself to hate Steve. Even if the torch he'd been carrying for Steve should've been extinguished and more than that, hacked into tiny pieces in Siberia, Tony had gathered up those pieces and carried them back home with him. Maybe pouring alcohol over them wasn't the best idea. It was flammable, after all.

He had the conversation he hadn't had with Steve in his mind, several times.

"Hi, Cap. I've been having these feelings about you. It's really weird. I'm guessing you don't have them. Can I get some of your DNA to do some science and maybe figure it out?"

It always sounded ridiculous, but most of the times, the imaginary Steve said yes. He might've said yes in reality, too. Maybe he would've been curious. Besides, he'd been handing out samples for all sorts of scientific experiments all his life.

In a moment of drunken clarity, it crossed Tony's mind that there was a chance Steve had already handed out a sample for amoromics at some point. Even if he hadn't wanted a soulmate back in the forties, maybe he'd changed his mind. Tony hadn't asked him about that, either.

He tapped on the coffee table in front of him to bring up a screen and a projected keyboard.

Technically, the only reasons anyone was allowed to access the database outside of routine matching runs were troubleshooting and research. Then again, he wasn't actually planning on doing anything illegal. If Steve had given permission to include his information in the database for matching purposes, it would get tested against every new database entry. Tony was just going to run yet another round of testing.

He breezed through the additional safeguards set up to protect data from VIPs. These were particularly high-profile individuals whose data wouldn't be offered for research use even in anonymized form, and wouldn't be shared across companies and countries to get higher population coverage, like regular entries were. If Steve was in the database, that was where he'd be.

That was where he was.

Tony opened the entry in plain text form and scrolled through an endless stream of A, T, C and G on the screen, marveling at the thought that these letters were the code that made Steve who he was. He ran a finger over a line, tracing it. What sequence would be the one that determined the particular pale shade Steve's skin? The blue of his eyes? The curve of his eyelashes? Where were the proteins whose expression levels the super soldier serum and the vita-rays had tweaked to turn him into Captain America?

And most importantly, was there, somewhere, hidden among the three billion base pairs, a particular sequence that was also in Tony's genome, the one could blame for his misery?

He could practically hear Bruce's voice calling him out for genetic determinism again.

He pulled up his own genome from his medical files. Even though he'd never entered it into an amoromics database, he'd had it sequenced. Of course. Out of curiosity, mostly, because why not. It hadn't offered any shocking revelations of his lineage or his risks for hereditary disease.

Tony hadn't worked with amoromics software in years; after the early days, he'd gone back to engineering, leaving the bioinformatics to the top specialists he'd recruited. Still, a quick online search and scrolling through a few pages were enough to remind him of the basics. Checking a single pair of subjects for INCS was a non-standard task, but not a particularly difficult one. Being drunk and out of practice wouldn't stop Tony from doing it.

A very quick check of the tools that they had on the development server revealed it was still all command-line. How quaint.

He typed the one line he'd need to start the quick matching pipeline, making sure he'd set all the parameters correctly. It didn't look particularly impressive.

He'd avoided doing this for four years.

Whatever the results, it'd be painful, and it wouldn't change anything; whether they were a match or not, Steve would still hate him and wouldn't want anything to do with him.

What the hell.

He hit enter.

The program started spitting out lines with information about the intermediary steps it was running. Tony could've figured out what they meant if he'd cared. He didn't.

He grabbed the bottle, took a big gulp, and leaned back on the couch. It'd take at least fifteen minutes to finish the matching. He'd need to be a lot more drunk than this to have the courage to check out the results.

Steve woke up in the early morning to an unfamiliar ringtone. It took him a few seconds to place it. Once he realized it was the one he'd set for the burner phone he'd sent to Tony, he was instantly wide awake, his heart racing.

The way things had gone down between them, something very, very bad must've happened for Tony to contact him. All that he'd heard of Tony during the weeks he'd spent hiding in Wakanda had been from occasional news items and the few reports Natasha had sent from home.

The sound had already stopped when Steve picked up his phone. The screen showed it hadn't been a call but a text message. He opened it right away.

BLAM score 100. e-value 1e-134. We're a match. My condolences.

Steve stared at the short message in confusion, and read it through several times. The values didn't mean anything to him, but he could only think of one thing that "We're a match" could possibly refer to.

He ran a quick internet search to check, and it confirmed his interpretation: BLAM scores and e-values were used to evaluate the probability of a soulmate match. A BLAM score of 100 meant exactly identical sequences, and the e-value was, as far as he could tell, some kind of estimate of how reliable a particular score was. The smaller, the better. 1e-134 was the same as 10^-134. That was astronomically small.

He'd figured out what the message said, but it still made no sense. He wasn't a match with Tony. They weren't soulmates. He'd had that checked. Why would Tony be doing this? To mess up with him and make him feel bad? Steve didn't think he'd be that petty, even if they were far from being on friendly terms.

It took him a while to realize he was still staring at the phone, and he could just ask. We can't be a match. I had that checked years ago. They didn't find anyone for me, he wrote.

He wasn't sure Tony would answer at all, so he was surprised when he did, almost right away. They wouldn't have. They didn't have my genome, Tony replied.

The revelation was like a physical weight landing on him, pressing him against the mattress. Breathing hard, Steve lowered the phone to his side and tried to unpack everything that this meant.

He remembered how he'd felt when he'd gotten the email about the matching results, and the exact words on the message: a negative result only means that you're not a match with anyone whose data is currently available.

If Tony's data hadn't been available, then Steve's matching results wouldn't tell anything about the two of them. He'd just assumed that Tony must've handed out a sample. Tony's company was running the whole thing, after all. He'd never actually asked Tony about that, though, or even told Tony that he'd taken the test. It wasn't the sort of thing you casually discussed with your teammates that weren't really your friends.

Your teammates that were your soulmates.

He tried to convince himself that Tony was lying to him to throw him off balance for some reason, but he couldn't imagine what that reason might be. Tony hadn't stopped him from breaking the other Avengers out of prison. He could've. Tony hadn't come looking for him. No matter how good Wakanda's defenses were, Steve was pretty sure Tony could've found him, if he'd really wanted to. There weren't many things Tony couldn't do if he set his mind on it. That was one of the reasons why Steve had always been so impressed by him.

At no point after what'd gone down between the two of them had Steve gotten the sense that Tony was out to get him or actively wanted to make him feel bad about what had happened.

Not that Steve hadn't felt bad, anyway. He had plenty of regrets. If they really were soulmates—if he could go back and do things differently—but he couldn't. It was useless to think about what he hadn't done, because he couldn't change it. He'd just have to work with what he'd got.

He picked up the phone again, and after a brief moment of hesitation, typed, Why are you telling me now?

There was no quick answer this time. Instead, there was no answer at all, although he waited for five minutes, then ten, and fifteen.

Beyond his window, the waking city bathed in soft morning light. Steve sighed, got up and dressed, heading for the communal kitchen. He kept the phone in his pocket, with the volume turned to the highest setting. He didn't expect Tony to reply, but if he did, he didn't want to miss it.

The kitchen was quiet, but not empty. Sam stood by the room-height windows, a mug of coffee in his hands. The view that opened outside was more alien than anything else Steve had seen in the future. It kind of looked like the way he'd thought the future should look: colorful and sleek and beautiful.

Sam turned to face him and gave him an appraising look. "Did something happen?"

Steve wasn't surprised if he looked a little shaken. He was. "Sort of," he said.

In a way, nothing had happened. Nothing had changed. Things were exactly the same as they had been before he'd woken up to that message. And yet, simultaneously, nothing was quite the same.

Sam was still eyeing him with some concern, but didn't push it. "There's coffee, if you want it," he said instead, raising his mug at Steve.

Steve really didn't feel like coffee. "Tony texted me," he went on, replying the question Sam had refrained from asking. "He thinks we're soulmates. Had it tested, too, and sent me the numbers to confirm it."

He half expected Sam to laugh at that, but he just looked thoroughly puzzled. "Huh. And you believe him?"

"Yeah. I do," Steve admitted. It made far too much sense, it explained far too much. Things had made less sense when he'd thought they weren't soulmates.

Sam set his mug on the table and crossed his arms. "But you've known him since you woke up from the ice. This isn't something that just happens to people overnight. If you never suspected anything…"

"I did," Steve said. He'd been almost certain about it, until he'd gotten those results that he'd falsely thought proved him wrong. "I bet he did, too."

"You and Stark," Sam said, shaking his head, looking like he didn't know what to think about this. "I don't get it. If you're right and you both had a hunch you're a match, then why didn't either of you ever say anything?"

Because Steve hadn't been sure what was going on. Because he'd thought he'd been wrong about what was going on. Because he'd thought Tony didn't want to talk to him. It all sounded like feeble excuses to him.

He didn't know what Tony's excuses had been.

"It was complicated," he told Sam.

If he'd have to guess, he'd say Tony must've suspected this for a long time, maybe from the day they'd first met. It'd explain why he'd always been so awkward around Steve, always on the defensive, hiding behind either actual distance or biting wit, never letting him close. He'd realized they were soulmates, and he hadn't wanted that. Maybe he'd even hoped Steve wouldn't realize it.

Steve wondered if Tony had only run the test now, or if he'd known about this for much longer, and only told Steve because something had changed.

He pulled the phone out of his pocket. Still no reply.

"So, what're you going to do about it?" Sam asked.

Even if Tony had messaged Steve, it didn't look like he was interested in actually talking about the situation. He felt a flare of annoyance at Tony for just tossing the information at him and then refusing to follow up on it. Steve wanted to grab him by the shoulders and shout at him to explain himself, but even if he rushed back home and did just that, he doubted he'd achieve anything. If Tony hadn't wanted to face the fact that they were a match before, he certainly wouldn't want to do so now, when he had so many reasons to hate Steve.

Steve shrugged at Sam. "I don't know. Maybe nothing."

He did, a few hours later, manage to catch hold of T'Challa to ask if there was any way they could make sure Tony was telling the truth. T'Challa said that technically, it would be a simple matter if they had access to Tony's DNA, but sequencing someone's genome without their explicit consent was so unethical, he'd only consider it if lives depended on it.

As far as Steve knew, they didn't have Tony's DNA lying around, and this definitely wasn't a matter of life and death. He would just have to take Tony's word for it.

9. Gene Therapy and Amoromics: Risks and Potential. 2016.

The practical challenges of designing such a "gene therapy" targeting INCS are considerable, but they're not insurmountable; the range of available delivery vectors is constantly expanding, as is that of tools for precise genome editing. Undoubtedly, sooner or later, someone will overcome these challenges. The questions we should be asking are about the ethical conundrums involved, since they extend far beyond those related to gene therapies aimed at curing illnesses and directly improving the subjects' quality of life. In itself, the presence of INCS in a person's genome is not a pathological condition. These sequences only have quantifiable effects when a subject is in contact with a matched partner. Although the mental and physical aspects of the resulting synchronization can certainly be distracting and uncomfortable, they're also transient and generally pose no significant health risk.

Why are you telling me now? Steve messaged him.

Tony didn't know what to answer.

Because the rules said so—when a match was found, both halves must be told of the results. Because Tony should've said something earlier, since he'd suspected this ever since he'd first met Steve.

Because he felt like he deserved to suffer, and telling Steve was yet another, particularly cruel way of tormenting himself.

He couldn't decide what to say, so he said nothing.

He drank some more.

At some point, he passed out on the couch.

When consciousness threatened to return, he tried to resist it. He really didn't want to wake up. He knew it would suck. He squeezed his eyes closed and pressed his face into the sofa cushions, but it was already too late.

The hangover and the regret and horror over what he'd done and what he'd found out last night coalesced into overwhelming nausea that went far beyond mere physical discomfort. He turned his head for some less stale air, keeping his eyes firmly shut. He considered making a break for the bathroom—he didn't trust the bile to stay at his throat—but the idea of moving made him feel even worse. He tried taking deep breaths through his nose instead.

He'd definitely drunk too much. It still hadn't been enough. He still remembered the test result. The one he'd known he'd get since he'd met Steve.

"Friday?" he called out. There was no answer. For a brief moment, he was alarmed, until he realized he'd shut her off himself. "Friday. Unmute. Cancel all my meetings for today."

"You sure, boss?" The AI's voice was softer than usual. She was smart enough to turn down the volume when it was obvious he'd been on a bender. "You've got one with Rhodey, you want to cancel that too?"

Ah, damn. His business associates and PR events and whatever else there might've been on the agenda could go to hell, but he wasn't going to fail Rhodey. Not again. "No. Not that one. How long before it?"

"Four hours, twenty-two minutes," Friday replied.

"Okay, I can do that," Tony mumbled. He pried his eyes open and rolled over to his side so he was facing the room.

The flip phone sat on the coffee table in front of him, mocking him.

He picked it up, his hand shaking so badly he fumbled and just barely managed to keep hold of it instead of dropping it on the floor. Thankfully, there were no new messages.

He wasn't ready to face Steve, to deal with all of his anger and disgust and disappointment. He didn't think he'd ever be. He'd have to, though, sooner or later; he couldn't avoid Steve for the rest of his life. Not unless it ended up being even shorter than he expected. What he needed was a permanent solution that was slightly less lethal.

Good thing he'd thought of one, a few years back.

He sat up. It sent the room spinning. He leaned against the couch back and closed his eyes again, focusing on his breathing. He really could've done without this right now. He had things to take care of. Of course, he had no one to blame but himself.

"Friday, bring up my notes on Project Alcatraz," he said as he waited for the worst of the queasiness to settle.

"I've got them right here," she said.

Tony decided to risk another try, opened his eyes, and leaned slowly towards the table, where the screen had lit up with the assorted files he'd asked for: several chains of emails with the gene therapy R&D people, a few plain text ones with DNA sequences, and the preliminary, proof of concept test results. That should be all he needed. It'd just be a matter of turning the plans into reality. Back when he'd been researching this, the people he'd talked to had assured him the wetlab work would be simple to implement. All they needed was a target sequence, and as of last night, he had one.

He opened the latest of the email conversations. "Is this lady still working for me?"

"Yes, and still on the same project, though she's been promoted," Friday confirmed.

"Even better. Let's give her a call."

He was done well before his scheduled appointment with Rhodey. He even had enough time to shower and grab a cup of coffee. He still felt like death warmed over, but that was a state of being he was well and thoroughly used to.

"Whoa, looking rough today," Rhodey greeted him.

"Just aging and alcohol," Tony said.

Rhodey pursed his lips. "You know, one of the two you can actually quit."

"My anti-aging cream provider would beg to differ," Tony joked, and went to fetch the leg braces so they could start setting them up.

The session was routine, and Tony kept getting distracted, which made him feel guilty every time he caught himself. He should've been focusing on Rhodey. Instead, all he could think of were Steve and the plan. He wasn't going to tell Rhodey about it—he was pretty sure Rhodey would try to talk him out of it—but he needed to make some kind of an excuse.

"So, I know we've got the next session scheduled for Thursday, but I might have to take a rain check," he said, casually, after they'd wrapped up and moved to the kitchen for refreshments.

"Oh? What's up? Unexpected business trip?" Rhodey asked, visibly surprised. Tony might generally be useless at keeping his booked appointments, but he'd been very careful not to miss any time with Rhodey, so he was definitely breaking the pattern here.

"Important biotech project that'll require my full attention for a few days," Tony replied. It was entirely true, if a bit vague.

Rhodey raised his eyebrows. "Biotech project? Should I be worried?" He nodded towards Tony, casting a pointed glance at the glow of the arc reactor.

"Nah, nothing like that," Tony said quickly.

Maybe too quickly, because Rhodey didn't seem entirely convinced. "Okay. So, we're still on for Monday?"

"Sure," Tony promised.

The entirely honest truth was, Tony couldn't really be sure. No one had done anything exactly like this before.

Almost every element he was using had already been tested in some other context: the pared-down version of Extremis, with far fewer side-effects than the original, was currently undergoing clinical trials, as was CRISPR/Cas, the gene editing tool that'd do the actual work. From what he'd gathered, at the worst, he might have to deal with a few days of flu-like symptoms—plus the consequences of modifying his INCS, which was the big unknown here. He'd purposefully designed the modifications so that the resulting sequences were unlikely to match anyone, assuming the current science that said INCS followed certain rules was solid. That shouldn't be a problem. People could live their entire lives without meeting their match, so that those sequences would remain dormant. As far as anyone could tell, lacking a soulmate wasn't fatal.

Forty-eight hours, that was how long his genetics lab had insisted that it would take to put together his project, and only if they assigned a few people to work on it full-time. He'd told them to do that. He'd also implied that it was a confidential Avengers matter; that should make sure no one else found out what he was up to.

He just wanted to get this over with.

He checked the phone. Steve had texted him at some point. Tony. I need to understand this. I deserve an explanation.

He ignored it.

He'd get back to Steve once he'd sorted this out. Until then, all he could do was wait.

Steve had never been very good at doing nothing.

Luckily, he had the exercise regime he'd set up to keep him occupied. The familiarity of it, the physical work and the challenges of training with some of Wakanda's finest were nearly enough to take his mind off what he'd learned.

Things were still exactly the same as they'd been. He and the other ex-Avengers were wanted criminals. Bucky was still in suspended animation. Tony had lashed out and tried to kill him. Steve knew he hadn't been thinking straight when he'd done that, and he knew he could partly blame himself and his decision to hide the truth from Tony, but that didn't make it okay.

Soulmates or not, all the bad blood between them wasn't going to magically vanish.

Only at night, when he lay alone in bed, his thoughts ended up returning to those old paths, making him wonder if there might still be a chance of fixing things. If he could, one day, stand next to Tony and feel companionship and warmth instead of the anxiety that had always been radiating from him.

He sent Tony a few more texts, asking him to explain himself, but Tony didn't reply.

The next morning, he felt slightly embarrassed he'd even done that. Why waste so much time and lose sleep thinking about someone who'd be happier if the two of them had never even met?

Sam asked him if he was okay, and he said he was. He'd dealt with far worse things in his life. It'd take some time to get used to this, but he would. It didn't change anything. No one even used the term soulmates anymore. Being a match with someone wasn't some deeply meaningful divine message. It was a biological coincidence, like a birthmark.

That night, he didn't even look at the phone, and if it took him a little longer than usual to fall asleep, that was because he had a lot on his mind, in general.

He was having breakfast on the third morning after Tony's text when the phone started ringing. It wasn't Tony, but an unknown number. That shouldn't have been possible.

He stood up and stepped away from the table to take the call, Sam's curious eyes on him.

"Who's this?" he asked sharply.

"It's Rhodes," came the unexpected reply. "Don't hang up."

"Wasn't going to. How did you get this number?" Steve demanded.

"Wasn't easy," Rhodes said. "For someone who supposedly doesn't give a damn about you, Tony sure keeps a close eye on that phone you sent him."

And no matter how much Steve had tried to convince himself he didn't care, he was struck by instant concern about what might have prompted Rhodes to contact him, and whether Tony was okay. He wanted to ask that, but settled for something more neutral. "Why are you calling me?"

"I'm afraid he's going to do something stupid, and you might be the only one who can talk him out of it." The way Rhodes said that, the very obvious urgency in his voice, did nothing to help Steve's concern.

"You don't think he'd try to—" The words 'kill himself' were on the tip of Steve's tongue, but he couldn't make himself say them.

Sam must've caught the alarm on his voice; he was now staring at Steve with a worried frown.

"I don't know what he's up to, but I'm sure it's not good," Rhodes went on. "He's been having a hard time dealing with all this. No matter what he says, the soulmate stuff actually means a lot to him. So. You're really not my favorite person and I know you don't give a damn about what happens to Tony, but you—"

"I'm coming over," Steve said, his mind instantly made up.

It would be risky, and he was pretty sure the others would tell him not to, but he knew it was the right thing to do. He and Tony needed to talk this through properly, for once and for all.

He'd already spent too much time doing nothing.

Tony hated waiting.

He sat through meetings and poked at projects, but his mind was constantly on what was to come.

Rhodey had clearly gotten the impression that Tony was up to something, which had made him annoyingly snoopy; he kept trying to make Tony slip up and tell him more. He got as far as a drunken confession that Tony had confirmed his match with Steve, but luckily Tony wasn't so drunk he'd blab the whole plan.

Rhodey must've recruited Pepper as well: she called Tony and demanded him to explain what mysterious Avengers business required several days of full-time work from a genetics lab. He refused to tell her. Luckily, he'd never mentioned his anti-INCS gene therapy idea to either of them when he'd first come up with it, so all they could do was guess.

When he got the message that the lab had finished putting together the thing—the Exvec construct, they were calling it—he suited up to fly over and get it himself. He half expected Rhodey to appear in full armor to stop him, even though he knew Rhodey's physiotherapist hadn't approved him to take it up yet. Instead, the short jaunt to the shiny new facilities in Boston went without incident. He parked his armor on the rooftop.

Stepping out of the elevator into the airy lobby, he could picture Pepper standing in the middle of the space in a crisp skirt suit, waiting to try and talk him out of it. Of course, she wasn't there, either. Not like she built her schedule around Tony's. Not anymore. Not in years.

It was almost as if a part of him were hoping for someone to try and make him rethink this.

In the end, the closest anyone came to that was the researcher who handed him the small, cooled transport container, gave him a curious look, and reminded him that the construct hadn't been tested on anything more complex than a cell culture. He told her he was well aware of that.

He flew back to the Avengers compound and retreated to his workshop, putting it in full lockdown mode.

The Exvec solution didn't look like much: a single test tube full of clear liquid that seemed slightly more viscous than water when he tilted it between his fingers. He thought it should've been more dramatic. Glowing like embers, maybe, like Extremis had. This wasn't Extremis, though. It was completely tamed, nothing left but a shell in which they could put whatever payload they wanted.

Since this was a complete shot in the dark, he could only try to guess what the dosage should be. He'd given it plenty of thought over the past two days, going over previous research, and decided to follow the original Extremis protocol. That meant serial injections adding up to a considerably higher dose than what the ongoing gene therapy experiments were using, but those tended to be targeted at some specific tissue. This wasn't. He needed to make sure he'd saturate his entire system with the Exvec construct, or it might not be enough.

The last time—the first time—Tony had had to put an IV on himself had been back with the whole palladium poisoning crisis. It wasn't exactly a well-practiced skill, and it took him quite some time to get it right. It might've also been that he wasn't in a particular hurry to get it done. He did get the saline lock taped to his arm eventually, without too much bloodshed.

He drew the first dose of the Exvec solution into a syringe.

The room was quiet around him. No phones ringing. No one knocking on the door. No mysterious signals from the universe, or from his few remaining friends, to tell him to stop. Of course, he'd muted all communications and had soundproof walls, so there wouldn't be.

He knew he was doing the right thing here, both for himself and for Steve.

He grabbed the tubing and pushed in the first dose.

He'd seen how it looked when people were injected with the original Extremis nanovirus, the screams of pain and the glowing skin. Just as he'd been promised, there was none of that, only a faint tingling and warmth at the IV site. He imagined he could feel the Exvec solution flowing along the vein in his arm, into his heart, then spreading all through his body, into every capillary, every cell, burning away those parts of his genome that said 'Steve'.

He realized he was crying. He tried to tell himself it was relief. It really wasn't.

It occurred to him that he couldn't be sure this had worked until he met Steve again. He'd have to set something up. An experiment. He'd need to find out.

The thought of standing in front of Steve and not sharing any of Steve's feelings did nothing to help with the tears. He felt like he wasn't breathing quite right, but he was pretty sure that was just emotions, not some kind of side effect. God. He was pathetic.

He took a shaky gasp and wiped his eyes with the back of his hand.

"Friday, time?" he checked.

"Two minutes since first injection," Friday informed him. "Twenty-eight to the next one."

"Damn, this is going to be a long day," he muttered. There'd be so much waiting.

He was itching for a drink, but even he wasn't quite reckless enough to add alcohol to the mix while subjecting himself to an unprecedented genetics experiment. He tried to distract himself with armor upgrade ideas, instead, but it wasn't working; his mind kept going back to all the times he'd fought side by side with Steve while wearing the armor, and the way he'd felt Steve's presence when he'd taken the helmet off.

When Friday finally told him the time was up, he could've sworn it'd been hours.

The second dose didn't feel any different from the first, going in, but maybe ten minutes after it, what had started as a barely noticeable headache, sometime between doses, had grown so painful, it was impossible ignore.

Not long after, the chills struck him, as if someone had turned the air conditioning to the max all of a sudden.

He'd known to expect something like this. He was flooding his system with a virus carrying foreign genetic material, after all. He got up from his desk, leaning on its edge, his head swimming. Once he was convinced he could trust his balance, he shuffled across the room to fetch a few blankets from the emergency stash, then curled up on the couch under them, shivering violently.

This was a bit worse than he'd thought it'd be, but he wasn't entirely surprised. Of course Steve wouldn't be easy to get rid of. He was the most stubborn person Tony knew. Tony would just have to be even more stubborn.

This time, he wasn't entirely sure if the way his breath caught at his throat was just emotions, or something physically wrong with his lungs.

He closed his eyes and maybe lost track of time for a bit, because the next thing he knew was Pepper's voice shouting "Boss," except that it wasn't Pepper, it was Friday. "Boss! Tony? Please let me call for help, your vitals are all over the place."

That sounded about right; he was too hot and too cold at the same time, panting and still light-headed from lack of oxygen, his heart pounding like he'd run a mile although he'd just woken up from a nap—he knew he was sick and it was probably bad, but he couldn't stop now. He had to suffer through this. For Steve.

He wasn't entirely sure why he was so sick, wasn't sure what was happening to him, but he remembered it was important not to let anyone interfere.

He started drifting off again.

There was a loud crash, and suddenly Steve was there, standing by his side.

He was hallucinating. He had to be. Steve couldn't be there, because Steve was thousands of miles away, and Steve hated him. Besides, Steve couldn't be there, not really, because it looked like he was right in front of Tony's face, and yet, Tony couldn't feel him at all.

Even in the Wakandan jet T'Challa had graciously lent Steve, much faster than any commercial airplane would've been, the flight seemed to take far too long.

Rhodes must've made arrangements for Steve's arrival, because instead of a group of costumed superheroes or armed guards, all that awaited him at the Avengers compound was Rhodes himself.

"He's locked himself in his workshop. I can't get through to him," Rhodes said urgently, in place of a greeting. "It's not like it's the first time ever he's done that, and maybe I'm overreacting, but—"

Steve suspected Rhodes could move fairly fast even in a wheelchair, but he didn't stay and wait to find out; there was no time to waste. He ran towards Tony's 'shop, doing his best to push away the thoughts of worst case scenarios, of finding Tony lifeless, unseeing eyes staring at him accusingly because he'd not flown over sooner.

The locked door was sturdy, but not quite sturdy enough to keep out an agitated super-soldier. Steve barged through into the room, looking around frantically. It wasn't difficult to spot Tony: he was lying down on a couch in one corner. Even before Steve got to him, he could see Tony's eyes were open and roving and his cheeks flushed. Definitely alive. He wasn't too late, thankfully. Something was clearly wrong, though.

Tony frowned at Steve, an unfocused, glassy look. "You're not real," he said, his voice breathless and hoarse.

"Of course I am. What's wrong?" Steve asked, placing a hand on Tony's cheek. It felt far too hot, like he was running a high fever.

"You can't be," Tony insisted, ignoring Steve's question.

Steve pushed back the blankets covering Tony, trying to understand what was going on. There was a short stretch of IV tubing taped to Tony's arm. He had no idea what it was for, but it couldn't be anything good. A chill ran down Steve's spine.

"Tony. What did you do?" he demanded.

Tony turned his head away, not facing Steve's eyes.

The voice of Tony's current AI assistant replied in his stead: "He injected himself with an experimental gene therapy to edit his genome so that it no longer matches yours."

Now that he thought of it, it occurred to Steve that unlike every other time he'd been this close to Tony, there was no echo of emotions that weren't his own. The only hint of what might be going through Tony's head was the tired, resigned look on his face.

Steve didn't want to believe it.

"He—he did what," he stammered, feeling like he'd been punched in the gut, the wind knocked out of him. "You can do that? Tony, is that true?" Steve's fingers clenched around Tony's forearm so tightly it had to be painful, but Tony barely seemed to notice.

"Better for both of us," he said softly.

"No," Steve said. It came out sounding almost like a sob.

He couldn't deny that he'd thought, over the past few days, that things would've been a lot simpler without those test results Tony had shared with him; if Steve's earlier belief that they weren't a match had been true. He'd also thought that maybe he could just ignore the whole thing, go on as if nothing had happened, pretend there was nothing special between them. Still, somewhere at the back of his mind, there'd always been that hopeful curiosity about things that could've been. Now, he'd missed his chance of ever finding out.

He'd never know how it felt to have a soulmate, and how all those descriptions he'd read held up to reality, not past the reluctant glimpses of shared feelings he'd experienced. He'd never know how it would've felt to hold Tony close and feel their bodies and minds fall into step with one another.

Tony's eyes closed, his breathing seeming to grow more labored by the second. The renewed pang of concern was enough to shake Steve out of his ill-timed brooding. He gathered Tony up in his arms. He had to get help, and make sure Tony got through this.

Matched or not, he still cared for Tony, just as much as he had before.

10. Societal Effects of the Increasing Rate of Genetically Determined Partnership. 2016.

Throughout history, there have been descriptions of couples who are more in tune with one another both mentally and physically than most. This gave rise to concepts such as the red thread of fate and the twin flames [1-3]. Since there was no way to identify the pairs of people who share this potential, such couples were rare, and aside from some anthropological studies, they weren't a common topic of scientific research. The discovery of genetic markers transformed the situation; more than that, it was perhaps the single most significant change in human mating behavior. While its effects on the individual level are often easy to quantify and have already been extensively studied [4-9], the wider effects on society are a much more challenging topic.

Tony didn't really lose consciousness, his grasp of reality just slipped. Not surprising, considering how awful he felt. It was like the worst hangover and the worst cold he'd ever had, getting together to unleash their demon offspring on him. The headache was so bad he couldn't think, his every joint ached, even his skin hurt with the fever burning through him, and breathing felt like drowning.

Somehow, between one blink and the next, he went from lying on the couch in his workshop, facing Steve, to a bed somewhere else, with more people around him, speaking in hurried, concerned tones, hands touching him, occasionally followed by a sharp sting. He tried to make sense of the words; they sounded familiar, but he couldn't focus enough to tell where one sentence ended and the next started, and even though it sounded like English, it could've just as well been nonsense.

He must've fallen asleep at some point, because the next time he was aware of his surroundings again, the voices were gone, and he felt slightly better, the aches and pains more distant, his lungs clearer.

His mind skimmed over the hospital details—the oxygen mask on his face, the pulse ox clip on his finger, the catheters stuck here and there—and latched on to the hand next to his. It was touching his just enough that he could feel the warmth of the skin, but it was also more than that. He could feel the concern and sadness of the person that hand belonged to, and even though his eyes were still closed, he knew without a doubt that it was Steve.

This was, somehow, a very important detail, though he couldn't tell why.

Tony moved his fingers ever so slightly to curl them around Steve's hand. He could feel the tap of Steve's pulse under his forefinger, and he realized it was perfectly in time with the background beep of the heart monitor. He absently wondered why Steve would be hooked up to one if Tony was sick. Was Steve sick, too?

This seemed important, as well, but he was too tired to figure it out.

He drifted off again.

The pieces slotted into place when he woke up the second time.

Steve next to him. Steve's concern. Steve's heartbeat matching his.

He'd been going to get rid of all that. He remembered thinking it had worked, too, in a feverish haze. He hadn't felt Steve anymore, and yet, now he did.

Steve's hand was still there, though it had moved, so that it was covering Tony's, big and solid and safe. Tony was half afraid that when he opened his eyes, he'd find out it wasn't real, after all, but it was: the first thing he saw was Steve sitting next to his bed.

Steve was wearing a dark hoodie, and his chin was covered in long stubble, like he hadn't shaved in a while. The look on his face was serious, a scowl, almost, but when his eyes met Tony's, his expression softened, a hint of relief blooming amidst the concern Tony sensed from him.

"Welcome back," Steve said, squeezing Tony's hand.

"It didn't work," Tony said. His voice sounded hoarse in his ears, though his breathing had definitely improved; someone had swapped the earlier oxygen mask for a nasal cannula.

"It didn't," Steve confirmed, as if it hadn't been obvious anyway.

Tony had been so sure it would work. In theory, it should've. In vitro, it had, but of course, his body was a lot more complex than a cell culture on a plate.

"What happened?" he asked.

"You nearly killed yourself, that's what happened," Steve said, anger flaring in his voice and in his mind. "And I found out that if one half of a matched couple gets seriously ill, that temporarily blocks the synchronization."

"Oh. Of course." Tony had known that. It was a defense mechanism, one that made a lot of sense. He'd just been too sick to think of it.

"Cytokine release syndrome, that's what they're calling your condition," Steve went on. "Which is a fancy name for some kind of seriously overblown immune reaction. Either to the modified Extremis virus you used, or because you targeted the soulmate sequences, they're not sure."

"INCS," Tony corrected, on reflex. "And just so we're clear on this, I wasn't trying to off myself." It was true. He hadn't been. Then again, Tony had to admit he'd been perfectly aware of the risks he was taking, and he hadn't really cared.

"Why do it at all, though? You hate me so much, you'd risk your life to get rid of me?" Steve asked. The raw emotions radiating from him were overpowering, but difficult to name: the anger was still there, but also other things, despair, longing, maybe fear?

Tony took a deep, shaky breath. His head hurt, and he was vaguely nauseous.

He needed to tell Steve that it wasn't about hate. That he'd done it because he didn't want to spend the rest of his life pining after something he couldn't have. He didn't even know how to start.

He realized Steve must also be catching some of his feelings, but this wasn't like telepathy. Steve wouldn't know what he was thinking. He supposed what Steve could catch would be just as confusing as what Tony was getting from Steve.

"Sorry, we don't have to do this now," Steve said, coming through ever so slightly disappointed when Tony hadn't answered at all. "It can wait until you're better."

"No. We should've done this years ago. It's time we got it over with," Tony decided.

He'd tried everything he possibly could, except for talking. There was nothing else left. He'd tried not to think about Steve, he'd tried to hide from Steve, he'd tried to cut Steve out of his very cells. None of it had worked.

He realized that he finally, actually felt ready to do this, to face whatever would follow, because there was nothing else left.

"Okay. If you feel you're up to it." Steve gave Tony's hand a pat, then let go and sat up straight, clearly steeling himself for what was to come, full of trepidation.

"Look, Steve, the thing is, I don't hate you," Tony began. "I've never hated you. After what happened, after Siberia, I tried. I really did. I wanted to hate you, you deserved that, for hiding things from me, but I couldn't. I—"

He couldn't quite make himself say aloud that he was in love with Steve; that would be too much, too soon. He didn't think he even knew Steve well enough to claim that. He loved some idea of Steve. He'd had a desperate crush on Steve since the day they'd met. He wanted to learn more about Steve, wanted to get closer to him, closer than he'd ever been with anyone, because thanks to the match, it would be unlike anything else he'd ever experienced.

Steve gasped, making Tony's breath catch, too, staring at Tony, his eyes huge.

Tony realized he'd just broadcast all that affection at Steve, all the feelings he'd always been so determined to push to the background. As confessions went, really, he might just as well have said the words.

"Tony—I had no idea," Steve said, almost like it was too much for him to handle. He reached for Tony's hand again, taking it between both of his.

Steve seemed to be consciously letting go of the anger and anxiety; Tony could feel it in the slow deep breaths Steve was taking, that Tony was subconsciously mirroring, although Tony's had a slight unhealthy rattle that Steve's didn't.

What surfaced was admiration and yearning, and warmth unlike Tony could ever have imagined. It was different from the furtive glimpses into Steve's mind that he'd had before, as if he'd always been eavesdropping and now they were finally in the same room, face to face, and he could hear everything the way it was meant to be. Steve's feelings weren't exactly the same as Tony's, a different color, a different timbre, but there was no mistaking what this was: Steve didn't hate him. More like the opposite.

"I'd no idea, either," Tony said, gaping at Steve. He was sure their shocked expressions were synchronized, too, in that moment. "I thought—ever since we met, ever since I started suspecting we must be matched, I always thought you wouldn't want that. I'd thought I wouldn't want that, either, until I met you. Then I realized I'd never wanted anything as badly, but I knew I shouldn't, so I tried to fight it."

"I didn't realize what was going on, at first," Steve confessed. "When I did? I used to think I didn't want a soulmate, but I was curious. I wanted to get to know you better and see if anything could come out of it. You made it very clear you didn't, though. Then I got those test results that said I had no match, and I thought I'd been wrong about the whole thing."

Tony wasn't sure where his own feelings ended and Steve's started anymore; it was a jumble of incredulity, relief, regret, and a million other things, everything that they'd been carrying around since they'd met, finally out in the open.

"If you'd just asked me," Tony said, shaking his head.

"Look who's talking! It didn't occur to you that maybe you should have a proper conversation with me before turning to potentially lethal medical experiments?" Steve said, his earlier anger returning. The force of it was downright scary through their bond.

Tony probably deserved it.

"Yeah, that was pretty stupid, now that you mention it." Out of habit, Tony tried to hold a casual, cool front, even though he knew Steve would see right through it.

"I'm glad it didn't work," Steve added, his voice still harsh.

"Yeah," Tony said. "You and me both."

They lapsed into silence for a moment, and the respite from all the intense words and emotions made Tony realize how thoroughly exhausted he was, the way his whole body ached like he'd been fighting a supervillain in a badly damaged suit, even though the battle had been entirely internal. He let his head sink back into the pillows, allowing his heavy eyelids to close.

Steve's hands were still holding Tony's. He ran his fingers up and down Tony's forearm in a soothing gesture. When he spoke up, it sounded apologetic. "Okay, I think that's enough for now."

"There's one more thing." Tony blinked his eyes open to glance at Steve. "The Accords, Siberia, all that."

"Tony, that can wait," Steve said hurriedly, with an instant flash of dismay.

It was kind of amazing, really, but Tony felt okay talking about that, too. Maybe it was because he was sick and probably on lots of drugs—not to mention that he'd just re-evaluated a whole lot of life choices he'd made, and realized how dumb they had been. It just didn't seem so important anymore, clinging to all the resentment, especially when he'd always known he'd forgive Steve sooner or later.

Tony reached out to take hold of Steve's forearm in turn. "No, it's okay. Really. All I want to say is, I won't hold a grudge if you won't."

"Just like that?" Steve asked, like he expected there to be a catch.

"It's in the past now, and I'd really like to move on." Tony tried to consciously push his acceptance and forgiveness at Steve, though he knew the synchronization didn't quite work like that. Maybe the feelings behind the ideas would at least be more obvious when he was actively focusing on them, and Steve would understand that Tony was being entirely honest about this.

Steve was quiet for a few beats, thoughtful and hesitant, but finally, he said, "Okay. I think I can do that."

They didn't talk about the Accords or the related crisis again during the rest of Tony's stay in the medical bay. Steve knew they would need to revisit the topic at some point, but he wasn't in a particular hurry to do it. They mostly didn't mention the other things they'd talked about, either, even though Steve spent most of his time in Tony's company. The medical staff encouraged him to do that; apparently, since Tony wasn't so sick that it'd block the soulmate link, Steve's presence was a stabilizing factor that helped him recover faster.

Now that they'd admitted it and were beginning to accept it, the fact that they were a match felt natural and familiar. Still, there was excitement in it, too. Like being around a crush. There was another long conversation there, waiting to happen, but having it in a hospital room wouldn't feel right.

Outside of the time Steve spent by Tony's bedside, helping him pass the time, he mostly hid in the room he'd been given, trying to lay low. He wasn't supposed to be in the country at all, let alone with the Avengers. Among the people who knew him, it was a bit of an open secret that he was staying at the complex. He had several conversations with Rhodes, most of them feeling like variations on a shovel talk, as well as Vision, who apologized that he had been elsewhere and unable to help when Tony had performed his unfortunate experiment.

It took two more days until the docs allowed Tony to return to recuperate in his own quarters. Steve suspected it might've been longer in most other circumstances, but since the distance from his hospital room to his own room amounted to a few floors, Tony could easily return for whatever follow-up tests they wanted to run. Steve couldn't blame the doctors for being cautious. What'd landed Tony in the med bay was entirely unprecedented, after all.

They'd sent a few of Tony's samples out for DNA sequencing, and confirmed that the experiment had had no detectable effect on his INCS in any of the tissues they'd tested. Not that it'd been a big surprise. Clearly, the synchronization effects between them were as strong as they'd ever been.

When Tony got the all-clear to leave the medical bay, Steve accompanied him on the walk across the building. It was the longest stretch Tony had covered after the incident. He insisted it was fine and that he didn't need Steve to hover so close, but by the time they were at the door to Tony's bedroom, he was ashen-faced and out of breath, the weariness radiating through their bond so profound that it made Steve want to lie down. He took comfort in the fact that he could actually feel it. That meant it couldn't be too bad.

Tony did lie down, landing heavily on his back on his wide, luxurious bed as soon as he'd reached it.

Steve lingered by the door. "I'll just leave you to rest, shall I?"

Tony turned to look at him, and all of a sudden, the air was electric with anticipation. "Or you could stay," he said hopefully, and patted the mattress next to him. "It's better for me if you stick around, you know. Scientifically proven fact."

Steve remembered that time they'd been staying at the Bartons', and Tony had refused to share a bed with him. He'd regretted it, back then. Now that the roles were reversed, Steve definitely wasn't about to decline.

"Sure," he said, walked over, and settled on the bed by Tony's side, propped on one elbow.

"So, I've been thinking," Tony said, sounding casual, his arms crossed behind his head—though Steve could tell he wasn't feeling casual at all. "This matching thing. We didn't really finish the conversation."

"Not really, no," Steve agreed, keeping his tone as light as Tony's. The excited energy between them was palpable; his heart was hammering against his ribs, and whether that was because Tony had been nervous or Steve was growing more so by the second, he couldn't tell. Not that it even mattered, the way their moods were merging together now that they allowed it.

"So, the question is, what do we want to do about it," Tony went on. The color was returning to his cheeks, and the look he gave Steve was openly flirty. "Because I've got some ideas, and I've gotten a certain impression from you, based on, you know," he waved a hand in the air between them, vaguely indicating the bond they shared, "but I don't want to jump to conclusions."

"You've jumped to some completely wrong ones before, but this time, I think you've got the right idea," Steve said.

He leaned closer and pressed his lips against Tony's.

No kiss Steve had ever had before could've prepared him for this; every ridiculous romantic fairytale about soulmates and their special connection suddenly felt realistic. It wasn't just that they were kissing and it felt good and right, like finally arriving somewhere he'd been trying to reach all his life, it was also that the excitement that had built up between them was amplified and reflected, reaching a new peak. There were no layers to their feelings anymore, just one overwhelming thrill that they were really here, together, when neither of them had believed it would ever happen.

Tony wrapped both arms around Steve, pulling him closer, clinging to him like his life depended on it. Steve didn't want to land on top of him, so he kept one elbow on the bed to balance himself, and placed the other hand behind Tony's neck, running his thumb over the coarse bristles of Tony's beard.

He'd never touched another man like this before; he'd wondered, sometimes, when he'd thought about Tony, back when he'd first guessed they might be soulmates, if it would feel awkward. It didn't. Probably, the matching was a part of that: Tony's skin was as familiar as his own under his fingertips.

When they finally let go, after what felt like several minutes, Tony was panting again, making Steve feel breathless, in a good way.

"Whoa," Tony said, sounding awed, a wide smile on his lips. "I think we may have hit the jackpot."

"How do you mean?" Steve asked.

"I've read plenty of papers about synchronization, and it's not the same for every pair," Tony explained. "This has to qualify for the more intense end of the spectrum."

"I certainly can't imagine it being much more intense," Steve said.

"If first base is like this, I don't think I've got the stamina for much more today," Tony said ruefully.

Steve ran a hand down along Tony's arm, took hold of his fingers, and brought them to his lips to kiss his knuckles. "That's fine. I normally wouldn't even kiss on the first date."

Tony chuckled. "Of course you wouldn't. So, I suppose this means you'd like us to be more than friends, then?"

Steve clasped Tony's hand between both of his. "It definitely does. There's just a few things that need to be sorted out first, like the fact that I'm a fugitive and not supposed to be here at all." He hated to bring any of that up right now, but since they seemed to be taking the first, tentative steps towards a future together, it couldn't really be avoided.

"Technicalities," Tony said dismissively. Steve could still feel his slight unease at the topic, both through the bond and in the way his fingers twitched. "I have an excellent legal team. We'll deal with all of that. Soon." Tony shifted to rest on his side, placed one hand between Steve's shoulder blades and hooked a leg around Steve's, pulling him closer again. "Right now, I'm still under strict orders to rest, and I'd really like to kiss you again."

"Okay, that sounds like a plan," Steve said, wrapping an arm around Tony's back.

Their second kiss was just as breathtaking as the first, if not more.