Set after the ending of Avengers Assemble.
Steve's P.O.V.
I walked into the lab where Tony was working. There was sweat on his brow which was furrowed in concentration. I could help biting my lip as I slipped onto the desk next to his work.
"Can I help?" A smirk spread across his lips as he looked at me and realised that I was in my uniform. "Nice to see you're still embracing the stars and stripes there 'cap'..."
"Put on the suit." I made sure my face was expressionless.
"Demanding." He put his screwdriver down and cross his arms. "Why should I?"
"Put on the suit. I want to finish what we started Stark."
"Stark? That's a little impersonal there Cap."
"Put on the suit." As my eyes motioned towards my crotch I watched his eyes light up.
"Jarvis. I need the suit and turn off the labs camera for a few hours." I raised my eyebrows as that fucking hot smirk spread across his lips again. "You're a lucky boy Cap."
I watched as he suited up, even though the metal cage hid his six pack it was all I could think about. I kissed him gently after I watched the red light on the security camera turn off.
He continued to kiss me as he slid the zip on the back of my suit down. He kissed down my neck and chest as he peeled the blue material off my body. "I need to spend less time in the lab don't I? Then again, it gives you time to work on these." He slipped back up to bite my lip as he ran his covered hand over my abs. The casing slid off as he slipped his hand into my bottoms, his touch was soft as his hand glided up and down my hard dick.
My moans grew as he got faster, pushing me to the brink. I opened my eyes briefly as he pulled his hand away, I growled lowly as he smirked. "I feel like taking the suit off. Is that okay with you Captain Rogers?" I smirked slightly and nodded, within seconds Tony was stood in front of me in his boxers, his boner was pretty obvious by this point and it didn't help the situation I was in. I slipped the remainder of my outfit off and stood completely naked in front of him. "Bend over cap." I nodded and obliged him.
The lab table felt cold on my naked torso but Tony's hands running all over me certainly made up for it, I gasped slightly as he entered me.
"F-fuck!" He pulled me up straighter and started to slam into me, the next few moments were filled with gasps, grunts and moans as he slammed me. I leaned back as his hand slid down and stroked me, I could tell he was getting close as he'd finally shut up. I let out one final loud moan as I came on his hand, the moan must have tipped him over the edge as I felt him cumming inside me.
We spent the next few hours exploring each other's bodies and figuring what we liked and disliked. It was perfect, he made me feel complete. As I fell asleep in his arms that night I knew that what we'd done had been right.
I also knew that this was the start of something beautiful.