These are Tony's favourite moments. He's punch-drunk with exhaustion, high off more caffeine than is really advisable for any living, breathing organism, and his mind is just coming down from that bright, crystal-clear edge, where math and physics and chemistry make perfect sense, the universe dancing at his fingertips. The portable containment field he'd just designed and put together cools on the table before him, sparkling with possibility; Tony isn't positive, but he thinks that he might have just saved quite a few lives just from this thing existing at all, capable of stopping the strongest plasma blast, the most explosive bullets, even Clint's arrows.
He's crashing bit by bit, but his blood still boils in his veins, his mind is still too restless, too consumed with variables and calculations and ripping his own creation ruthlessly apart, putting it back together until it's perfect, more than perfect.
...So okay, these are not his favourite moments; but hey, just, wait.
The door swooshes open and soft footsteps pad nearer, just loud enough not to startle. Tony knows without turning that the interloper comes to stand right behind him; he can feel the warmth of their -- oh, who is he kidding-- his skin, the ephemeral scent of citrus and vetiver, the huff of breath that teases the small hairs by his left temple.
He doesn't speak, and neither does his visitor, just stands there, tall, solid, patient like a fucking rock where Tony is concerned, which is something Tony still can't quite wrap his mind around. Tony just leans back, a little to the side, feels the step Steve takes forward to take his weight, to brace him when he needs it, always, even when Tony didn't know he needed it so badly he was dying with it.
Steve noses at his temple gently, presses those plush, sweet lips of his to the tired skin at the corner of Tony's eye, curls his hands over the edge of the table before Tony, boxing him in with sure, dependable arms.
"Done?" Steve says, low, no more than a murmur, vibrating through Tony's back to curl up in his chest.
"Yeah," Tony replies, hoarse, fading fast. He leans back further, goes boneless, trusts Steve to catch him like he always does, always will.
Steve sounds relieved; Tony wonders how many hours he's lost down here, how much restraint Steve had to employ to not come down and drag him out, to let him work when Tony's on a roll. Sometimes Tony doesn't understand what he's done to earn this--trust, this caring; those are the times when Steve kisses him like this, slow, soft, rubbing their lips together, nipping at Tony's lower lip when Tony lets his head fall back, turns into it. Steve kisses him like they have all the time in the world; like nothing else exists but the two of them, here, amidst the mess of spare parts and dirty cloths and the smell of grease and leather and machinery.
These are the moments when Tony can let his doubts and fears and crippling inadequacies go; the moments when he gets the fleeting edge of thought, that maybe he doesn't have to earn this -- that maybe it's Steve's gift to him, something he doesn't have to earn, just accept.
When his body drops him into unconsciousness, as it inevitably does, pushed beyond all endurance, it is with the taste of Steve's lips on his that Tony falls, lets go, loses himself in the warmth of Steve's arms, the scent of him, safe, home.