A/N: Originally posted as a response to an ask prompt on my tumblr (aworldofpretty).
The first time he's on top of her it's during a mission. A bomb ticks down and he slams into her, knocking her to the ground and landing on top, shielding her from the blast. She buries her face in his shoulder, closes her eyes tight, fists her hands in his vest and holds on to him.
Afterwards he lifts his head and she meets his eyes and it's a moment before he finally draws away.
The second time he's on top of her it's a fire fight. Bullets are flying and she's in the way, so he spins them, presses her into the wall with his body against hers. She meets his eyes and he returns her gaze, the two of them locked in each other while May takes out the enemies.
He doesn't pull away immediately. She whispers thank you under her breath and he nods at her and for one moment, one confusing, beautiful moment, he lets his lips brush her forehead. It's comforting, soft, everything she needs with her heart pounding in her chest and the blood rushing past her ears. It calms her almost instantly.
The third time, it's deliberate.
They're sparring, her striking out at him and him deflecting each hit with a single-minded purpose. She lashes out to hit his face and he catches her wrist and yanks. She stumbles, hits his chest with hers, and she's right there and so is he.
So she kisses him.
He stills for a moment and she thinks this is it, he's going to push her away, find her a new SO, something, but he doesn't. He fists a hand in her hair, wraps another around her and pulls her close against him, sealing his lips against hers and kissing her harder.
She exhales against him, relief and happiness and pleasure, and his hand slips up under her shirt. This isn't a romantic first kiss, it isn't something leading to a relationship, it's pure desire, fuelled by the life-and-death situations they'd been in, by all the times he'd pressed into her to protect her and all the times they'd sparred.
He lifts and lowers her with one motion, pressing her back into the ground and kissing her harder, hand slipping around to the front of her shirt and pushing up underneath, his calloused fingertips seeking her soft skin.
She arches her back, pressing up against him, and he takes the opportunity to push her shirt up more, leaning down and kissing her stomach and following the hem as he lifts it.
She wonders if she should tell him to stop, they're exposed here, anyone could walk in, Coulson could walk in, but all she can focus on is the way her skin burns under his touch and his kiss, like he's igniting it.
He kisses her neck and she drops her head back, running her hands up under his shirt. He catches her wrists, pins them above her head and she gasps and stares at him. She knows she could stop him, tell him to let her go, but she doesn't want to, she just wants him.
He draws back after a moment and his hands find the waistband of her sweatpants, pulling them down her thighs. He kisses her skin as it's revealed and her breath catches. She wants to catch him for another kiss, lather him with the attention of her lips, tongue and hands, but he's undoing her too quickly for her to be able to function long enough to take back some control.
He presses a kiss to her underwear and she bites on her lower lip then releases it. "Grant," she breathes and he looks up at her and kisses her again, her lips this time, his hands catching the sides of her underwear and starting to pull it down.
"Okay?" he murmurs against her mouth and she nods and wraps her arms around him, pulling him closer with her nails dragging up his back. He groans into her mouth and she catches his lower lip between her teeth, tugging lightly.
He lifts her knees, bending them and pressing between her thighs, hard and hot against her through his pants. She closes her eyes, lips parting, and drops her head back again and he watches her almost reverently as one hand finds its way between her legs, one finger then two slipping inside of her. She's warm and wet, like she always is when they spar or work out together, and he kisses the side of her neck and flicks his thumb as he moves his fingers. She quivers underneath him and her eyelids flutter as she makes noises he swallows with another kiss.
He pulled back and undoes his own pants and she tries to sit up but he knocks her back down. She hits the floor and the air leaves her lungs and he crawls on top of her with his pants undone. She can't see because he blocks her gaze with his chest and she wonders if it's deliberate for a moment, and then he's kissing her again, one hand lining himself up and then other slipping under her bra, his fingers pressing gently against her soft breast.
She reaches down, digs her fingertips and nails into his back and pulls on him, begging without words, and then he slips into her and her back is arching and she cries out, quiet and gasping.
He catches both her hands and pins them above her head, pressing down on her and kissing her again as he moves his hips slowly. She closes her eyes, surprised by how slow and gentle he is, and rocks her hips in time with his, running her hands lower to dig her nails into his ass and pull on him.
He pushes down on her harder and starts moving faster inside her until she can't think straight anymore for the how good it feels. His fingers rub against her, other hand pinning her down, and she's gasping and shouting, not a single thought or care given for the fact the lab is right there.
He groans and grunts but makes no more sound than that, watching her intently and never closing his eyes, and she comes with a shout as pleasure pulses through her body. She gasps, quivering underneath him, and he pushes faster until he buries his face in her neck and goes completely silent and still.
She raises a hand, his grip lax now, and strokes her fingers through his hair.
He's still on top of her but it's different now. They had sex just moments before but now it feels intimate. She kicks her pants off her ankles and wraps her legs around him, not letting him slip out of her yet, and her other arm circles him.
Neither of them move for a couple of minutes, his face pressed into her neck, and then he draws back. "We should finish training."
"I agree." The moment is over, there's no point clinging to it. She pulls her pants and underwear back on and up and watches him as he gets to his feet and buckles up his belt, then takes his hand when he offers it out, letting him pull her up.
She smiles at him, he smiles back. It's a silent moment between them. Nothing will change unless they want it to, that's what they're saying.
He lets go of her hand. "Let's practice your punching," he says and turns away.
"I'm just glad you didn't say fisting," she replies and he laughs, he actually laughs.
She smiles and steps over to the bag.