"Hi, Mr. Stark, I'm (Y/N)," you held your hand out to the man that Nick Fury had told you so much about. He was that genius, billionaire, playboy, something or other guy who was apparently a pretty big deal.

"No, no, that will never do," he smiled as he took your hand then turned to lead you into the tower, "you call me Tony. Got it, kiddo?"

You glanced back to Nick nervously, wondering if you were making the right choice in joining the team. You definitely weren't the most outgoing person, and if this was a group of strong personalities you might just drown within them.

"Yes, sir."

He stopped just short of the door and turned, looking at you incredulously, "they told me you were a fast learner?"

"Tony," you sighed, "I'm sorry. Tony."

"Atta girl."

~~~

"(Y/N), it's just physics. How are you not getting this?"

"Excuse me?"

Tony moved around the lab table to stand at your side, putting his arm around you and his hand on your shoulder as he pointed to the screen before you with the other. "Okay, let's dumb this down...." his voice trailed off and he looked at you cautiously, waiting for the slap that would surely grace the back of his head. "That was a poor choice of words. I'm gonna pay for that in some subtle way later, aren't I?"

"It's not gonna be that subtle," you sighed.

He turned back to the screen, trying to keep his mind on the lesson and not the revenge that you were surely plotting as he spoke. Your mind was definitely working on your plan and you were lost in your own thoughts. Every so often his voice would break through with words like 'kinematics' or 'astrophysics' and other terms that really meant nothing to you, but he was so animated when he spoke and was so passionate about his work that you couldn't help but appreciate at least that much.

"So, what do you think?" he asked, eager to hear if you finally understood.

"I think you get way too excited about this stuff, Tony." You reached up and put your hand on his face, quickly giving him a kiss on the cheek before stepping away. "But sorry, old man, I still don't get it."

"Fine," he sighed, "then don't expect me to learn any of that pathophysiology junk that you're working on." He waved his hand dismissively and turned back to his computer, "as long as this temple of a body is working, then that's all I need to know."

"You do realize that 'temple of a body' uses the laws of physics just as much as one of your suits, right?" You gave him a smug smile as he did his best to ignore you, looking suddenly very interested in whatever was on his screen. "The energetics of metabolism, turbulence of fluid flow in the heart and lungs, and the acoustics of sound waves? Would you like to discuss the principles of regulatory feedback in the central nervous system, perhaps?"

You stood next to him with your arms resting on the table, leaning forward towards him to get him to meet your gaze, but he didn't acknowledge you, still doing his best to stare at a screen that he hadn't touched in several minutes. "Tony? Is that the face you make when you're losing?" You reached out and closed his computer, looking at him with your best mocking pout.

"Would you like me to dumb it down for you?"

~~~

Several days later you spent the day with Clint, working on target practice while waiting for Tony to return with Steve and Thor from their quick mission only a few states away. Since you had arrived at the tower a few months ago, you made it a point to spend time with each of your teammates individually; not only did you want to know them better, but it was the best way to gain enough comfort to not feel so shy and awkward around them. Joining the team had been intimidating to say the least, and if it hadn't been for Tony, you may have already quit.

"Alright, Nat's coming in to work with you on guns. That's her specialty," he said, putting his bow back into the storage closet. He walked past you to the target and pulled the arrows free, inspecting each tip for damage and sighing when he found one that he couldn't salvage. "You need to get better fast, girl. This is costing me more than I expected."

"You can get more."

"But I love these," he mumbled, "they're my favorite."

You rolled your eyes, grabbing your weapons from your bag and sitting on the bench to load them. "Alright, ya big baby. I'll buy you more, okay? I'll bring my own from now on." You pulled off your jacket to change into a lighter top for the shooting range, but before you could remove your shirt, Clint broke out into a fit of laughter.

"Where did you get that?"

"Ugh," you groaned, "Stark. It's ridiculous, but if I'm not wearing it when he gets back I'll never hear the end of it." The tshirt you were wearing was covered in small drawings of different body parts; the heart and brain were actually kinda cute. The random foot, ear, and occasional inappropriate body parts weren't so great; across the front were the words 'Biology Nerd' in huge gold letters, covered in glitter. "I lost a bet."

Before he could ask for details, you heard the jet coming in for a landing. Natasha hadn't arrived yet, so you decided to welcome the group before you got started and to see how everything went. You barely had the door open to leave when the sounds of running and yelling filled the halls.

Clint gave you a worried glance and followed you out, running towards the hangar to see what had happened. You felt your heart pounding in your chest, hoping that it wasn't anything too serious and that it was merely the two of you misinterpreting the sounds that you were hearing.

"Tony," you gasped when you opened the doors and saw him, lying quiet and bloody on the gurney as Steve helped push him towards the infirmary. "Steve, what the hell happened? You said this would be an easy trip."

"Come on, we can talk on the way." As he continued to walk ahead, he glanced at you over his shoulder and you swore you heard an actual giggle from the Captain.

"Nice shirt."

~~~

It took three hours for them to finish working on Tony and suturing his wounds back together, but you'd never know he was even injured; the man rarely stopped talking, especially around you. Maybe talking about the battle or continuing to get you to understand physics, or insisting that you admire his will to live through such traumatic injury was his own way of distracting himself from what was happening.

"Why do you look so sad?" he asked, "was it something I said?"

"No," you answered quietly, your eyes averted to the floor, "I was just really scared when I saw you, that's all. You looked pretty banged up, Tony. I know you were scared too, I could see it in your eyes. And when you're nervous your left lower eyelid twitches."

He looked away and smiled sadly, taking a deep breath and now matching you in avoiding eye contact. "I think we hang around each other too much, (Y/N). You're learning my secrets."

"Is that a problem?"

"Hell no," he answered almost immediately, his head snapping to look at you now, "it's great. You've really grown on me, kid."

"Okay," you sighed, leaning back in your chair and rubbing your hands nervously on your legs. You were terrible at talking about feelings and emotions, and really felt much more comfortable with sarcasm and humor, but there were things that needed to be said. It felt like now was the time. "I'm going to go down an uncomfortable path, so this might get bumpy."

He put his bandaged hand up as if to stop you, "hey, wait, you're going to talk about feelings, aren't you?" The word looked as if it hurt him even to say it.

"Yeah," you said as you grabbed his hand and forced him to let you hold it, much against your instincts to let him pull it back. "Listen, Tony, you know that I lost my dad when I was really little, so I can't remember ever even having one. And I think that's why you and I have bonded so quickly. You've really treated me like I was your own, and I just need to say thank you."

"To me, you are."

There was an uncomfortable sting in your eyes and you knew this could get messy. It was about to get full of tears and blubbering and just general puffiness in your face that you never wanted anyone to have to witness. "Tony, stop."

"You know that my family life was shit, let's just say it like it is, alright? And then you get dropped off at my door like some obvious answer of what my life was missing." Tony reached over and lifted your chin with his other bandaged hand, making you look at him. "You are my own, (Y/N). Nothing is ever going to change that." He released you and smirked, "not even your mortifying choice of attire."

"Oh, that's how it is?" you said with a smile, thankful for his change in tone.

"That's how it is."

"Well, Stark," you paused, reaching down into your bag that you had brought from your session with Clint, "I just happen to have....this." You held a shirt up for him to see, equally as ugly as your own, also covered in small drawings and large letters across the front.

Tony's eyes widened and his face grew serious, "No."

"Yes." You stood up and held the shirt up, slipping it over his head and helping him put his arms into the sleeves, despite the constant groans and annoyed sighs. "There," you stepped back to admire his new look, "the ladies are gonna love it."

"Physics Geek?"

You moved to stand next to him and put your arm around his back, holding your phone in the air, "Smile, old man." The picture snapped before he could take the phone away, and you hurried to grab your bag to leave. "Not so subtle, remember? Bye, dad!"

His mouth hung open as the door closed behind you, slowly changing to a smile at the sound of your laughter and the nice ring that 'dad' had to it, even if you said it as a joke.

~~~

The common room filled with the sounds of multiple phone alerts, with the team getting your picture simultaneously. Steve looked at Natasha, who looked at Clint, and he looked at Thor, all knowing what they had to do.

"Twitter, everyone?"