Received this as a prompt on tumblr. Enjoy!

Steve wasn't exactly sure when it'd started. He would think about it sometimes, late at night in the soft blue glow of Tony's arc reactor, halfway between dreams and reality until it all blended together. That's when he could remember it best. It was like an open veil between two worlds, and the memories would slip out from their little niches in his mind and play out in front of him like a movie on the screen.

It'd begun after they'd started dating, when they'd first started spending the night at each other's places. The first few times they'd spent the night together, Steve found himself unable to sleep. And when he eventually did, it was a fitful slumber. He'd roll around, agitated, waking up frequently. He felt exhausted every morning, and it had nothing to do with the activities that took place before bed.

And so, to give himself something to do while he waited for sleep to find him, he would stare at Tony's arc reactor. At first he'd done it out of curiosity. Sure, he'd seen the device before many times, glowing from underneath Tony's shirt, or shining as what had become a national symbol of hope and perseverance, from his Iron Man suit. But he'd never really looked at it before.

Carefully, tentatively, so as to not wake up Tony, who slept so little as it was, he'd leaned in close to Tony's chest, his eyes following every inch, every line of the glowing device. Until he fell asleep looking at it, his head resting on Tony's chest.

After that he grew a little bolder, although he was always careful not to disturb Tony. He began tracing his finger along the metal, and found it surprisingly cool. Like he'd done with his eyes, he used his finger to trace every inch, feeling every single indent and change in texture. It was meditative almost, and as before, he'd fallen asleep without knowing it, his head resting against Tony's chest.

It wasn't until a few weeks later that Steve figured out it was BECAUSE of the arc reactor that he couldn't sleep. Steve had always slept in complete darkness. Shades shut, door closed, TV off. He even flipped his phone over while it charged at night. He'd been that way since he was a kid. He'd never been afraid of the dark, and had taken out the night light his parents had put in for him. How Steve didn't make the connection faster, he didn't know.

When he told Tony about it, Tony immediately designed a cap of sorts that he could click onto the arc reactor at night like a magnet, and effectively block its light.

But then Steve realized that he missed the light. He couldn't sleep through the night without it. It turned out to be more than that, though. He needed the light now. The first night without it, he'd woken up at 1:15 in the morning in a cold sweat. He'd been having a nightmare. It'd been a combination of his time in the war, losing his best friend Bucky, mixed with Avenger missions gone wrong where one of them got hurt, and a cold morning on the Thames river...

He'd looked over at Tony's side of the bed out of habit, and it was as if the world had stopped spinning when he didn't see the glow of Tony's arc reactor; the very thing that was keeping the person he cared about most in this world, alive. A few dark tendrils of his fading nightmare still clung to his mind, making logical reasoning difficult, and for a few horrifying seconds he thought Tony was dead.

He had grabbed Tony, and shouted his name, images of Bucky dead, fellow soldiers lying wide-eyed and vacant, dead on the field, the chill of the Thames, all flashed through his head again, dreams and reality slipping together. Because when you left the veil open, not only the good things slipped through. The dark ones crawled out, too, from the crevices where they'd been left to fester.

It was the first time Steve had ever seen Tony Stark well and truly scared, his face stripped of all other emotion. Just pure terror. Tony had faced intergalactic beings, armor-coated monsters that flew through the skies of New York, insane gods, and a hundred other things that would make the bravest of men tremble. And he had laughed in the face of them all, or grunted in pain, but he always had a witty line to thrown at the enemy, and a positive out-look at the end of a battle. Usually suggesting they go eat at some hole-in-the-wall restaurant that none of the other Avengers had heard of, and Tony'd never been too either, but somehow knew the name and location of.

Tony wasn't afraid for himself. No. He was afraid for Steve, the man who'd gone to sleep in the middle of a war, and woken up 70 years later to an alien world. He was afraid for the man he was starting to fall in love with. The first person he'd ever trusted with his heart. The first person's heart he wanted to be entrusted with. The person who had saved his life when no one else knew how far in the shitter he really was.

"So, no more cap?" Tony had joked weakly when they'd both settled down. Steve had personally melted down that black cap himself, taking almost too much pleasure in its demise.

And from that day forward, Steve woke up at exactly 1:15, and peered over Tony's shoulder, where he had him pressed up against his chest, to see the glow of the arc reactor. He would touch it, because he had to. Had to know he wasn't dreaming. Had to know it was real, and working. And that it wouldn't stop working.

Steve had taken the job a little too seriously for a while after the "Incident" as they referred to it. He would stay up all night, watching it, making sure it didn't sputter out. He was afraid that if he fell asleep, it would go out. Tony had noticed how haggard Steve had become again in the mornings, and when he finally pulled the truth out of Steve, he threatened to make another cap to put over the reactor. That stopped Steve's protests pretty quickly. However, it didn't stop Tony from lovingly referring to him as 'Guardian of the Arc' for awhile after that.

However, Tony didn't know that Steve still woke up at the same time every night to check the reactor. It was six years later, and they were married and living in the same house together now. He didn't stay up all night anymore, but still, he had to check.

And that's what he was doing now. Tony's chest rose and fell evenly as he slept. Steve stared at the reactor, gently running his fingers over it. He could feel the energy it gave off now. It was tangible to him.

He'd just begun the process, when he realized Tony's chest was rising higher, and sinking deeper, no longer rhythmic. He looked down at Tony's face, and saw dark brown eyes, wide and alert, carrying no weight of slumber.

Steve stared back, unsure what to say or do. Tony smiled, one corner of his mouth twitching as his smile threatened to turn into his signature smirk.

"What are you doing, Captain?" he asked quietly, his tone hinting on playful. Like he wasn't at all surprised to find Steve touching his arc reactor. And after a second, Steve realized that's because he wasn't.

"How long have you known?" Steve asked sheepishly, his big blue eyes apologetic. Because that was Steve. He took everything to heart in that great, big heart of his. Even when he had no reason to.

Tony smiled in full now, to show that he didn't mind what Steve was doing. It was about privacy, Tony knew. Steve thought he was invading Tony's privacy by doing what he was doing. Which was ridiculous, because they'd been together for over six years, were married now, and he let Steve invade his privacy and space almost every night, and many times during the day as well. In any place that they wouldn't get caught, and several that they did.

"You mean how long have I known you've had a fetish for my arc reactor?" Tony joked, giving Steve a cheeky grin. "A few nights," he said, his smile dimming down to a softer one.

"I can feel it, you know, when you touch the reactor. It's a part of me," Tony informed his husband. He ran his own hand over the reactor, looking down at it for a moment, before looking back up at Steve. "It feels a bit like you running your finger along my palm. It tickles a bit. But it's nice."

Tony took Steve's hand in his, and ran the tough pad of his index finger along the sensitive skin of Steve's palm. A smile instantly jumped to Steve's lips. It did tickle.

"Is it because of the 'Incident'?" Tony asked, letting worry color his voice as he watched Steve's face closely, looking for any hints he might find there. "Is it like before?" Before, when Steve stayed up all night. Before, when Steve had nightmares of the past.

Steve shook his head.

"No?" Tony cocked an eyebrow. He pushed himself up to a sitting position.

"Well, yes," Steve said, unconsciously adjusting his position to keep his hold on Tony as he moved. He wet his lips. "But I realized, just earlier this week actually, that it was more than that. More than just the nightmares. Do you remember the Thames?"

Tony nodded hesitantly. "How could I forget? That's where the beginning of our epic love tale started. Or will start, when you regale our grandchildren with it," Tony joked, trying to make light of the situation. But it came out sounding more wary than humorous.

"Well, there's a part I left out of that 'epic' tale of ours," Steve confessed.

Steve had found Tony washed up on the shores of the Thames river in London, England seven years ago. They were there on a mission for the Avengers. And for the rest of the Avengers, 'There' meant Aberdeen, Scotland. For Tony Stark, 'There' meant the Thames.

There'd been a party held in their honor after they'd finished the mission. And toward the end of the night, Steve noticed Tony was no where in sight. He'd only realized it because he'd been having a pleasant, undisturbed evening that wasn't filled with the cutting remarks of a certain billionaire, genius, playboy, philanthropist. Or should he say, he wanted it to be pleasant. It should have been pleasant. He shouldn't have missed the incessant chatter and digs from a certain "Man of Metal" so much.

You see, Tony and Steve didn't exactly get along when they first met. Steve was a team player. He believed in teamwork, and charmed everyone around him so that even the most independent of souls, found the togetherness pleasant and satisfactory. It was impossible not to like Steve. He was so kind, warm-hearted, and loyal, that you just wanted to take him home and cuddle him. Or at least find a pocket-sized version of him that you could carry around with you wherever you went. He was a trained leader that everyone would give their hearts to follow.

Tony Stark was not a team player, and no amount of smiles and words of encouragement and pep talks could change his mind. Tony was a leader simply because he didn't want to follow anyone else. Tony could charm a room in a second, could make them laugh with his witty remarks, but he didn't want their hearts. Didn't want their devotion. He cared for only one person, and that was himself. And well, maybe Pepper, too. As a result, Tony Stark was not the person you would follow into a battle, but he would be at the forefront anyway, shouting commands even if they contradicted that of the actual Captain.

Which he did often. Much to Steve's annoyance. They never saw eye to eye, and bickered "like an old married couple" as Clint had so lovingly put it.

Things changed when Steve traced Tony's whereabouts to London, where he pulled him out of the river where he'd been floating in his Iron Man suit. It apparently had a flotation device. Tony had been drunk-off his ass, passed out. That wasn't the first thing Steve noticed though. What he noticed first was that Tony's arc reactor wasn't glowing.

Steve panicked, because he knew that could only mean one thing. Reflexively, he pinched Tony's nose between his index finger and thumb, and pressed his mouth to Tony's, giving him his breath. Then he pulled back and placed his hands on Tony's chest, and pressed down. He wasn't sure how CPR would work on Tony, but the arc reactor put up no resistance. He pressed his mouth to Tony's again when he didn't respond.

After what seemed like several lifetimes, Tony began coughing up water, his arc reactor flickering back to life. He breathed in and out heavily, gasping for air.

"Not how I imagined our first kiss, Captain," were the first words out of Tony's mouth, playful as ever despite the fact that he had nearly just drowned.

Steve was so relieved that Tony was alive that he grabbed his face between his hands and kissed him. Tony didn't respond, either because he was too shocked, too tired, or too numb to feel it. But it didn't matter, the kiss wasn't a romantic one. It was like when you cried because you were so happy. It was purely celebratory.

It wasn't until later, when they were both alone, that they touched their lips, running their fingers over the thin skin where it still tingled.

And that's where the 'epic love tale' began. It didn't have a pretty beginning. Steve had found out just how bad Tony's drinking problem was. He'd diagnosed him as a 'high-functioning alcoholic'. Which meant he could function completely normally in public and around friends and family. He could work and go to events and save the world, and make everyone believe he was fine.

Most people didn't know that there were different types of alcoholics. And the fact that Tony could still function so normally, just fed the problem.

"A gift," Tony had declared, making a grand sweeping gesture from where he was sprawled out, half on and half off, Steve's couch back in New York, like he meant to take a bow. And then proceeded to spill his cup of scotch down his shirt.

The middle of the tale wasn't a whole lot better. Steve's struggle to get Tony sober. Both of them struggling with newfound feelings for each other that had been growing beneath the surface for a long time before, but were starting to sprout through now that they were being given attention. Albeit, unintentional attention, but it grew none the less. But it had its moments.

It was the latter half, and the half that was still being written – and would continue being written for a long time to come if Steve or Tony had anything to say about it – where things got brighter. This was the part that they wrote about in fairytales. Although, still, for Steve and Tony, there's was more likely to be a Grim's Fairytale than a Princess and the Frog one. It was when Steve finally helped Tony to sober up. Well, as much as Tony Stark could sober up. It was when, on a warm summer night, on Steve's apartment deck where they were watching the folks below dancing to the music in the square, that Tony looked across the table at Steve, and told him that he was in love with him. Because Steve was quiet, and gentle, and he liked his privacy, liked his little hidden moments. It was when Steve proposed to Tony at the unveiling of the Captain America statue in Time Square. Because Tony was loud and flashy, and he loved a good show. It was when Steve held Tony close every night and stroked his fingers along the arc reactor that kept his husband alive.

"You never told me that," Tony said softly, his eyes searching Steve's. "I never knew that the arc reactor had turned off when you found me in the Thames."

Steve shrugged, because he couldn't explain why he didn't tell Tony. He couldn't explain it because it was a feeling he'd had. It wasn't tangible. He couldn't put it into words. He didn't even know himself, really.

But the image was forever burned into his mind. And it was something he never wanted to see again. Could never see again, and survive. It was why he did what he did. Why he had to wake up and make sure it still glowed.

Call it OCD or ridiculous or whatever you wanted. Steve didn't care. All he cared about was the way the blue glow of the arc reactor was playing across the thick gold of Tony's wedding band, where Tony's hand rested next to it on top of Steve's.

"I understand," Tony said. And he did. Because as much as they still argued and got on each other's nerves, because they were still Tony Stark and Steve Rogers, and they would never not get on each other's nerves, they could always read each other. They knew what every twitch of the hand, every shift of the shoulders meant. They knew how to push each other's buttons. The bad ones and the good ones. And the very, very good ones.

Tony rested his head against Steve's chest, and Steve pulled him in closer. That night they both fell asleep in the soft glow of the arc reactor. And, couple months down the road, Steve will find that Tony has sewn a patch onto one of his Captain America suits that says: "Guardian of the Arc". He will find this out in the middle of a nation-wide, televised interview, when the interviewer asks him about it. And Tony will smile wickedly from his safe spot in the front row of the audience, while Steve will smile through the question, and explain it away easily, because that's what he did. And later that night, Tony will pay for it dearly in the bedroom.

Started off a bit angsty, but then got cuter at the end, aye? What'd you think? Thanks for reading :)