A/N: I don't usually ship Tony/Natasha, but I got a prompt on Tumblr, asking me to write this, so yeah, enjoy.
DISCLAIMER: Everything in this fic does not belong to me, unfortunately. They belong to their rightful owners: Marvel, Stan Lee, etc.
"Can I ask you something personal? If this was the last birthday party you were going to have, what would you do?" Tony asked, his magenta button up shirt, already buttoned, save for a few at the top as he sat down in his chair, his arms resting at the armrest, his legs spread wide as he looked at Natasha.
"I would do whatever I wanted to do, with whomever I wanted to," Natasha replied, looking straight into those brown orbs of his. Tony might have gotten what she said definitely wrong because before they both knew it, Tony's lips were against hers, kissing her ferociously as he backs her up into the nearest wall.
Natasha didn't hesitate, she knew that what they were both doing now were out of pure want and need. She had a mission to do, and right now, that mission was the last thing on her mind as Tony's lips moved over to her neck, sucking and licking to get a small moan out of her. Once that happened, he smirked and moved his lips back up to hers, kissing her slowly.
Tony ran his hands up and down her legs, stopping at the end of her dress before lifting it higher to reveal more skin. Natasha was at his mercy now, she didn't even want to argue or deny what was about to happen. She was finally realizing, firsthand, that Tony was definitely going to be great in bed – or wall.
Natasha had enough of this, she ripped apart Tony's button up shirt, buttons flying everywhere as they land on the floor. She saw the lines that were spread across his chest, starting from the arc reactor. She knew what was happening to him and it hurt that she wasn't able to do anything about it…yet.
"I'm sorry, we shouldn' –" Tony began as he saw the way she was looking at his reactor. He wasn't able to finish due to Natasha kissing him as she unzips her dress and letting it fall to the floor. Tony just had to pull away to admire her in just her lingerie, not like he hadn't before, but seeing it in person rather than on a computer screen was way different. He smirked and lifted her higher, her legs immediately wrapping around his waist.
He began kissing down her neck to the middle of her chest before going back up to meet her lips. His hands roamed freely across her body and were loving the structure of it, of her curves and love handles, how smooth her skin was. He was caught by surprise when Natasha cupped his him through his pants. He shut his eyes and leaned closer to her hand, his forehead resting against the crook of her neck.
Natasha smirked and unbuttoned and unzipped his pants, letting it fall around his ankles, evident that he was already hard. She couldn't help but laugh when she noticed that he was going commando. Typical Tony. She took his already aching member and stroked him slowly, wanting to drag out a moan from him. Once that was accomplished, she raked her hands across his back, loving the feel of muscle under her fingertips.
She was caught by surprise when Tony tugged down her panties and thrusting into her quickly. He quietly moaned at the feel of her around his member. He hadn't done this in a long time and he knew it was going to be over even before it started.
Natasha instinctively wrapped her arms around his shoulders to bring him closer, loving the width and length of his member inside of her. She shut her eyes as he continued to thrust into her slowly.
"Oh God, Natasha…" Tony said against her collarbone, biting down lightly as he continued to quicken his movements, gripping her hips so that he could ground into her more forcefully.
Tony gripped her hips tight as he thrust upwards and came. Natasha yelled his name aloud as her body went limp and they both collapsed atop of each other on the floor.
Then one thing registered his mind: Pepper.