So this came to me while I was reading some Avengers/Big Hero 6 crossovers. I thought it'd be a fun thing to write, so here we are. I hope you enjoy reading this!

Oh, if someone can figure out what they're calling mutants or superpowered individuals in the MCU, please tell me because I thought they had a specific term for it but couldn't find it so I'm using metahumans as a placeholder until told otherwise.

Prologue

Shiro stretched as he glanced over to his left. He was sitting atop a building with Wanda beside him. The two of them were waiting for the call from Captain America that they were a go to enter the building to support the team inside. As usual, Shiro felt something twist apprehensively in his gut in regards to the thought of the mission he was sent on. It didn't take a genius to know the reason either.

They were there as support, or well, Shiro was. Wanda was there to assist in the infiltration. Shiro was the impromptu medic of the team considering his vast medical knowledge. Medical knowledge he didn't recall ever learning in his life, which wasn't saying much considering up until a year ago, Shiro's life consisted of a lab and a containment unit. The lab was to study him, while the containment unit was to protect the people studying him from his lethal flames.

Shiro didn't really care for remembering the lab he'd spent two years in so he shoved it to the back of his mind while he concentrated on the mission instead.

Wanda Maximoff, or Scarlet Witch as she was known as informally, reached over and gave his shoulder a squeeze. "It will be fine. You'll be fine. Just breathe, Sunfire."

"Easy for you to say," Shiro gave the woman a lopsided smile, "this isn't your first mission."

"No, you're right, but it won't be your last." Wanda gave his shoulder a small pat before she stood and looked around. "Rogers and Romanoff should be in position now."

Shiro nodded and stood himself, his hands briefly going to the pack that was on his hip with medical supplies. He had to be careful. While he couldn't be harmed by his own flames, the supplies within could be and he didn't want to try and work on someone with half his supplies useless due to heat damage or being ashes, nor did he want to test how fireproof Stark had managed to make the material of his suit. Therefore, he was determined to direct his flames as much as possible to his hands and defending himself.

A small buzz in his ear snapped his attention back to the present. His hand went up to press on the button of the small earpiece in his ear. "Shiro, Wanda, you have three in the floor below you. Another four are currently in the target area."

"Copy that Romanoff. Good luck."

Silence met his ear as soon as Wanda spoke, and Shiro let out a breath he hadn't realized he'd been holding. Three agents below, with another four within the lab space they were about to hit. No pressure. He glanced over at Wanda before he focused on the door leading in. Striding forward, he followed Wanda as she made her way down.

It was ridiculously easy for him to help the woman take down the agents on the floor below, his moves swift and fluid as he went through the strikes and patterns he recognized as karate. Where he'd picked it up, he didn't know, but he was willing to bet it was in that span of time before the lab. He glanced over to Wanda as they made their way down the stairs to the next level. She might have had more experience with being an Avenger, but Shiro definitely had stealth on his side.

Strikes and kicks. That was all he allowed himself to do since he still didn't trust his flames enough not to cause lethal damage. Stark had joked that he was like a cat that jumped when they sneezed. Shiro couldn't agree more about the assessment of his own apprehension of his abilities.

When they meet up with Natasha and Steve in the lab, Shiro had succeeded in probably spraining his ankle but at least had been able to dodge fast enough to avoid a spray of bullets. Thankfully Wanda had been there to prevent the young man's head from being blown off with a well-timed shield, so he wasn't about to complain about that. Honestly, he could have thought of a thousand other ways this could have completely gone wrong. Not the least of which was if he had accidentally lost control of his abilities and set fire to the building during a freak-out.

Natasha went to work with the computers, something Shiro felt the urge to help her with but refrained from, while Wanda looked over the lab for other files stashed away. Steve had left briefly to check over the rest of the building before returning to the room. "Sam's got an eye on the surroundings to check for any people making their way back. We should have about ten minutes before someone decides to try and crash this location."

Shiro was leaning against the window, looking out with his arms crossed to prevent him from trying to go over and… Do what? Try his hand at hacking? He knew he was good with computers, but again like with his knowledge of health care, he didn't know how he got the skill.

Natasha nodded. "Well good. We have plenty of time then. Stark's present to these guys froze them out, so it'll take me five to retrieve what we need to." She glanced over to Shiro. "Unless Jumpy over there is too skittish to stick around, that is."

"Be kind. It is his first mission, after all. He didn't do too badly." Wanda waved a hand as she finished gathering the sheets on the desk with the other. "Besides, I would bet he might feel as though he wants to do something other than stare out the window."

"No, I'm fine." The words slipped out of his mouth and he shook his head. "I just don't think I've ever been shot at before. So, yeah…"

Natasha merely nodded, working quickly while the others worked to gather the intel they had been sent to find. Shiro helped, having been given a brief summary of what they were supposed to be looking for. He couldn't help but read some of the files he was gathering and swallowed. Metahumans. There was information on metahumans in the files, and he shook himself before continuing with his duty. Deal with this first, he reminded himself. Other Avengers were taking on the other facility, the more heavily-guarded one. This one was child's play.

Three years ago he had awoken in a lab. He'd had no name, no memories, and worst of all, no clue as to why he was there to begin with. He'd tried to fit what was going on around him with anything familiar, but had realized it was an exercise in futility. Wherever he was, he wasn't anywhere familiar. That knowledge amplified the moment Shiro laid his eyes on the scientist.

From then on, his life became a cycle of tests, sleep, and more tests. He discovered his inner fire the first day, when they stressed his mind and body to the point of breaking and an inferno engulfed the containment unit he was held in. It didn't last long, the oxygen in the unit running out before serious damage could be done leaving Shiro gasping for breath and his mind hazing. When they finally allowed air back into the unit, Shiro was left with a feeling of complete dread. Such tests continued for weeks, months.

They never spoke to him, not really. They only called him Subject T, and gave him orders he had to obey. He tried his best to obey them, simply because the moment he refused to, they would cut the air supplied to his unit and leave him struggling to breathe. He learned quickly that he hated the feeling of drawing in air and never getting enough into his lungs.

He didn't know how many tests they performed, or how much they pushed him, but he knew that eventually they progressed to performance tests, endurance tests, the likes. He discovered that his flames didn't harm him, nor did any others. They did harm others, much to Shiro's horror when they dragged in people to test them on. He refused, time and time again, and each time, they deprived him of oxygen.

Eventually he wondered how much brain damage he had suffered during those tests.

It was during a raid on the lab that he discovered how long he had been in there. The Avengers had decided to investigate Hydra's bases, and the moment that the scientist had tried to order Shiro to attack, the young man had crossed his arms and refused. He knew the scientist wouldn't kill him, hadn't in all the time Shiro had been a captive.

It had been two years. Two years worth of trials, experiments, blood draws, samples, things that would haunt Shiro's sleep for years to come. The Avengers, not knowing what to do with him, had cuffed him and taken him out for questioning, and Shiro hadn't resisted. All he'd asked was that if they had finally come to find him.

It was discovered when they raided the lab's notes (most of which were purged from the system) that Shiro had no name, no identity, nothing to say that he ever existed outside of the lab. Whoever he had been before was gone, leaving Shiro a nonentity. He hadn't even had a name to go by, only Subject T, and he absolutely refused to be referred to by that name. The team that had discovered him hadn't come to save him, he'd found out. No one had known he'd existed to begin with.

In the weeks that followed, they searched everywhere they could for a missing person's report that matched his description. Shiro could only provide that he was obviously of Asian descent, that he was (surprisingly) fluent in Japanese, and that sometime before, he'd studied medicine. It was only later, when he had met Tony Stark, that he had discovered a new facet to himself he had never known.

He was surprisingly adept at engineering, robotics, and programming. He'd immediately started asking about the mechanics behind the Iron Man suit, studying it with a critical eye and pointing out things that he'd thought were obvious, but everyone but Tony was confused about. That had led to the then unnamed man being directed through the tower blithely by Stark, a cautious Romanoff right behind them, being given the tour of his open labs. Shiro had no doubt that there were other, more private and secure labs that Tony never mentioned.

Stark had also been the one that suggested the name Shiro to him, since the young man was a blank. Shiro had been confused at first, until the meaning of the word, not the name, hit. White. Pure. Untainted. Shiro was a completely innocent person, no matter what had been done to him in the labs. He had no prejudices, no hate (other than what had been done to him), and no mistakes of his own. It was a fresh start, and as Stark aptly pointed out, Shiro deserved one after what had happened.

The only requirement that was issued was that he had to see a therapist. He went, if for no other reason than he was curious as to why, and he quickly found out. They had originally suspected him of being a Hydra plant, which nearly had the young man laughing at the idea until Romanoff pointed out he could have conditioning that no one was aware of. She of course was the most wary around him, and he wasn't about to blame her for it either. He didn't remember anything before the lab, and Romanoff could easily be right about him.

Shiro sat, rubbing his face as he looked around the living quarters of the Avengers base. He'd been left to himself, with mostly his thoughts to keep him company. That, and a TV remote that had him lazily flipping through channels. He settled back, frowning as he flipped to a program discussing something about some kind of future tech and rolled his eyes. The information was correct, if a bit vague, but Shiro couldn't help but shake his head.

They were crediting a young kid for the advancement in magnetic bearing servos, but Shiro couldn't help but correct them. How, he had no idea, but the kid hadn't created them. "No, that's not right. That was Doctor Robert Callaghan, founder of the Laws of Robotics. He invented them."

"Who invented what there?" Shiro's head snapped to the side, and Tony was standing in the doorway, head cocked to the side as he took a sip of something from a tall glass. "Oh, I hate those shows. Never get their info right. I mean, don't get me wrong, kid's a genius, but one of my old colleagues was the one that invented those."

"You know Doctor Callaghan?" Shiro blinked in surprise, but shook his head soon thereafter. Of course Stark would know the guy.

"Knew him. Guy had a mental breakdown when his daughter was involved in some kind of accident. Ended up stealing some tech from a student and setting fire to the exhibition hall that killed one of his other students." Tony walked over and put his drink down. "I'd feel sorry for him, but killing a kid? Not cool."

Shiro frowned. "So, where is he now?"

"Currently? Serving a sentence of thirty years in a penitentiary for manslaughter, attempted murder, arson, and destruction of property." Tony stuck his hands in his pockets and looked Shiro over. "So, I was thinking that since you're part of the boy band now, maybe it wouldn't be a bad thing to get back amongst the land of the living."

Shiro cocked an eyebrow. "Hasn't that what I've been doing, actually being back around normal people?"

Tony snorted. "Because running around in spandex and setting things on fire is considered normal. Well, maybe for Cap and Widow, but not normal for most people." Tony shook his head. "What I was meaning was that you have a good brain, kid, and you've obviously got something of a higher education under your belt. Why not use it?"

Shiro muted the TV, a frown pulling at his features as he studied the older man. "Maybe because I don't exactly have anything like identification or legal documents stating I'm even alive? I know that people have been trying to look for who I was before, but nothing's come up yet."

"Don't worry, the legal stuff's being taken care of." At Shiro's incredulous look, Tony shrugged. "I have an entire army of lawyers that I can call and I don't use them often, unless it's to disprove yet another paternity suit. I had some of them look into the issue of your legal status, and since no one can find out who you are and you're stuck in limbo because of it, I figured I could do something."

Shiro blinked. "Isn't that difficult to do? I don't even have a birth certificate or social security card."

"This is why I came up with the idea of getting you both. Right now you're what, early to mid twenties? Generally you'd be right, but there are ways of getting you some things so that you can actually function. So far, you could get a temporary number if we could prove your age, which is the trickiest part of this whole mess." Tony smirked. "However, no matter how tricky, I'm pretty sure I can make it work."

Shiro crossed his arms, not believing for a second that Tony was going to pull any of this off. After all, he had run through every possible way he could reclaim something of a life, and had run across the very problem that Tony said he could solve. "How do you even know I was born in the US though? I could have been born anywhere."

"One, you have a California accent. Northern Cali, probably the San Fransokyo Bay area considering the high concentration of Japanese Americans there, since you don't exactly sound like a SoCal guy. Plus, you have a phenomenal grasp of robotics and programming, which is quite common from someone from the technical schools in the area." Tony looked at Shiro appraisingly. "So either you moved to the US from Japan and studied here since you were a baby, you moved to San Fran from elsewhere and grew up there, or you're a native of the area."

"And all of that information still doesn't identify who I am, does it?" Shiro slumped, not liking the implications. "What if I just happened to be hatched in a lab somewhere? I mean, there was nothing on the databases when you hacked in regarding anything about me."

"Except from what I was able to get from SHIELD, they had just acquired you three years ago." Tony looked unbothered by Shiro's implication that he was created. "Humans don't spring fully-grown from labs. You, my friend, are a kidnapping victim. Who you were before, we haven't been able to figure out yet. When we do, you can bet you'll be the first to find out."

And that was the sticking point for Shiro, wasn't it? For everything that had happened, he wasn't sure he wanted to know who he was now. His bout with amnesia aside, it wasn't like he was unhappy with his life. Frustrated, yes, but hardly unhappy. He didn't know what he was supposed to do if he found himself with his old life again.

Something on his face must have tipped Tony off that Shiro wasn't exactly thrilled with the idea of finding out about his past, so the older man patted him on the shoulder. "Hey, don't worry about it. Whoever you were before, it doesn't change who you are now. Remember that."

Shiro wasn't sure if he could be comforted by that.

Natasha rubbed her forehead, going over the encrypted files carefully and running them through the program Stark had designed specifically for this sort of job. So far, each file had to be sent in individually since from what she could tell, they were all chopped up and placed everywhere within the database she had downloaded them from. There had to be a rhyme to the madness she was seeing on the screen, but she couldn't yet. She considered asking Stark to take a look, but considering the information on the files, she wasn't sure that she wanted him to see it yet.

"Looks like someone's burning the midnight oil down here."

Natasha glanced up and noticed Sam Wilson strolling over to the computer, a steaming cup in hand. She nodded toward the man and cocked an eyebrow. "Please tell me that's straight black. I could use the jolt right now."

Sam nodded and set the cup down, cradling his own in his hands as he glanced over the program running. "I heard from Steve that you're down here, and I figured you'd need it. How's the decryption going?"

"Slow and painful." Natasha took a sip and savored it. "I'm thinking of finding the person responsible for the encryption and making their death slow and painful."

Sam winced as he sat down backwards on the chair next to the desk. "That bad, huh? What do you think we're looking at with all of it?"

"From what I can tell, they're patient files. Possible subjects they were working on. Not sure entirely but…"

"You don't want to get Shiro's hopes up that we might have found information on him." Sam nodded in understanding. "I might not have been part of the strike team on that one, but from what I read, they did a file dump on everything."

"That they did." Natasha's eyes glanced back to the screen and shook her head. "I don't know why they thought they needed this much security on their files though. Not unless they had something big planned, which from what I thought, they don't."

"Maybe they've decided to come up with something else since the helicarrier incident. I mean, that was a large plan we disrupted of theirs." Sam shrugged.

"So was Sokovia. We don't know what they were planning, but we know they were working with enhancing humans. That much we know about from Maximoff. She told us they used the scepter to enhance them." She shook her head. "The problem is, the events in Sokovia don't add up to the events last year. It was a separate event."

"Unless it wasn't." She frowned at Sam, who shrugged. "Look, we'd been raiding Hydra bases all last year, and the one we ran across that had the twins looked like a solid operation that had been going on for a while."

"And they could easily transfer subjects from one facility to another in the interim." Natasha could already see where this was leading. "You're thinking that Shiro might have been one of the ones moved and the others in these files happen to be other surviving test subjects?"

"Makes the most sense." Sam frowned. "But there's still something missing though. He said he woke up in that facility. In all that time, he hadn't moved at all. The twins weren't either from their location, and from everything we could tell, neither had the scepter."

"Two different processes…" Natasha was already working through everything in her head, and the result wasn't pretty. "If you're right, then that means that there's another process to make enhanced humans, and Shiro might have been one of the subjects of that." She leaned back and glared at the screen. "You know, between Steve, Thor, Wanda, and Banner, I almost feel like I'm a lot less of a threat than they are."

"Almost?"

She ignored the wry tone in his voice. "Almost. They obviously either weren't human to begin with, or had something happen to change them. However, they didn't go through years of training in the same stuff that I did. Well, except for Thor. He's got centuries on me." She focused her attention on the screen again before looking over at Sam. "In any case, we're looking at super-powered individuals being suddenly injected into the equation. Like they're upping the ante. How long before they find enhanced humans willing to work with them?"

Sam considered that for a moment and winced. "I don't want to find out. I really don't. If and when they do, it's not going to be a pretty fight. And wings or not, I'm still human. I can take those off and just be another soldier. We're all very breakable compared to some of the others."

Natasha nodded. "Yes we are which is why we don't go barging into fights. We strategize, we plan, and we make contingency plans for when we end up over our heads. But we still fight."

"You're going to make me start looking for Tony's stash in the building with this kind of talk."

"It's an open bar. It's hardly a hidden cache." Natasha smirked, before looking at the screen again. The computer had dinged, alerting her to one of the files that had been decrypted. She glanced at it and sighed. "Nothing but notes. Granted, notes are good, but…"

She stopped, her brows furrowed as she read through the notes. "Random mutation?"

Sam glanced at the screen as well. "Found the other process?"

"Just notes on people that spontaneously develop strange abilities." Natasha flipped through the notes. "So far, according to this, they located thirty six different people with them." She glanced at Sam. "Want to make a wager that our resident amnesiac's one of them?"

"Do I really want to be making bets with you? I've seen your poker face."

"Hey, when you can manipulate the god of lies into revealing information, you use that gift." She shrugged. "Besides, I have a feeling this was where the files that were dumped were sent a year ago."

"So now we've got random people developing powers?" Sam snorted. "Way to make a guy feel impotent."

"I can think of worse things." She stretched, loosening muscles made tight by the position she was seated in. "In any case, this just got more complicated."

Sam nodded. "Yeah, because if that's the case, then there's no telling who's going to be a metahuman or not."

Natasha hummed in agreement, eyes narrowed as she considered the notes before her. "In any case, we need a way to find out who they are, where they are, and if Hydra's got an eye on them as well."

Shiro frowned as he was handed a packet by Tony, who seemed completely nonchalant about handing the younger man a large manila envelope. He looked from Tony to the envelope, then back at the older man. "Um, what's this?"

"Admission papers." Tony waved a hand at the envelope and went over to the drink station in the main area. Shiro had been reading quietly when Tony had entered, and he watched as the older man poured himself a drink before settling down next to Shiro. "I decided to ask around and found out when the next term starts. You kid are not going to let that brain go to waste."

Shiro blinked and shook his head, trying to wrap his mind around what was going on. "Wait, admission to where?"

"MIT, my alma mater. They're going to make you take placement tests, but I'm pretty sure with what knowledge you already have, you'll blow them out of the water." He took a drink before he set the glass down. "You have a lot of potential kid, and all of it is going to go to waste if you just do nothing but sit around the base."

"But I have no records. How am I getting around that?"

Tony snorted, looking affronted. "Oh come on. You doubt my ability to talk to the admission board? They know your situation, they know you have no memories, but they also know that you're really intelligent. You're at least halfway through a master's level for engineering, if not there already. You code like no one else I've seen except me. You can keep up with my techno-babble. If you have to start over with some of what you know, so what? You're at least in the door."

Shiro looked a bit unconvinced. "I can't go by just Shiro, and I refuse to go by Subject T."

"Which is why you're not going with that stupid name." Tony waved a hand at the envelope. "Go ahead, open it up, read my genius at work."

Hesitantly, Shiro opened up the envelope and pulled out the forms. His jaw then dropped as he read the name across the top of the first one. "Shiro-"

"Stark. Congrats. It took a bit, but I finally managed to figure out a legitimate way to return something of a life to you." Tony raised his glass in Shiro's direction. "I know my dad's got to be rolling in his grave right about now, but at the moment, I don't see a problem with it all."

"You adopted me?" Shiro sounded incredulous. "But I'm an adult. That's-"

"Quite legal to do. You technically fell under the diminished capacity category, and considering that we knew your relative age, it wasn't hard to come up with a birth date for you." Tony then crossed his arms. "Well, are you going to fill them out or what?"

Shiro stared at the paperwork for a moment before he looked back toward Tony. "Thank you. I just, I didn't expect this."

"Well, it was either this or get something completely ostentatious and unnecessary for the anniversary of your rescue. Which now happens to be your birthday." Tony then looked serious. "It may just be temporary, or it might not be. Either way, you have a place to be until that does or doesn't happen." Tony then grinned. "Now I get to find Pepper and hear her yell at me for a bit about going behind her back again and doing something completely out of the blue."

Shiro sat back and regarded the information in front of him when Tony left. It was like an impossible dream. He was about to go to one of the top technical schools in the world, he had a birthday, and while it sounded strange, somehow he'd gained a family. Maybe this meant that his life was about to turn around.