There is something about Tony Stark that Loki cannot quite put his finger on; he is, quite possibly, the most human of all the Midgardians that Loki has come across, with his foils and failings and the bright, staggering wealth of emotion that Loki still cannot grasp.
(he wants to take them apart, these tiny little people with the fragile skin and bird-like bones and see just how they manage to contain all that feeling, because Loki was certain that as you travelled further down the evolutionary chain intelligence and emotive comprehension got smaller and less, but he is ancient by the reckonings of humanity and he has known many species of which humans are most definitely the least physically impressive, and yet they seem to feel more, a paradox of sympathy and empathy versus physical space and he wants to take them apart to see if they really are bigger on the inside)
Tony Stark is a tumult that people only ever see as the eye of the storm of his own creating; but Loki can see everything that he ever was in the beads of sweat fine across his skin, can taste the fury and the desperation and the way his mind is constantly pushing at the tiny confines of his human boundaries. He is an addict, to drink and danger and sex and the constant battle of arrogance versus self-betterment in the eyes of those around him that tastes like whiskey and soft cold loneliness in breath that stutters across skin.
His blood tastes of palladium and vibranium and iron and a thousand other things that wash over and under and all around one another, complimenting and defying and defining one another and if Tony Stark is an addict, he must surely equally be an addiction because Loki has no reason to keep returning to him other than that Tony Stark tastes raw and mortal and alive and he cannot get enough.
Sex in Asgard was never like this, sex in the air and in the sheets and sinking into his skin so that everything reeked of it and sex reeked of everything in an endless, heady cycle. Loki had never been able to open another person like this, to have them shaking and gasping and staring at him with eyes blown impossibly dark like he was the whole world and the answers to all of the mysteries of the universe. It feels more powerful than holding someone's life in his hands, being looked at like that, as if Loki holds everything in the clench of his muscles or the roll of his hips or the flick of his tongue.
(and Tony never bats an eye at how Loki likes to ride him, and that's not just because Tony prefers to top but also because he doesn't seem to care that Loki needs to be in control and be taken care of simultaneously within that; and it could be that they make the perfect comparison because Tony wants to relinquish control and Loki just wants to take all of it and stay wrapped together like this for an eternity but humans are mortal and short-lived like a flap of a moth's wing, and so they do everything with an impatience and a haste that sets Loki on fire inside with their desperate push of now now now)
There is no one else in all the universe for whom Loki would pause and consider when Tony asks,
"I want to see you. All of you. The real you. Please,"
and then let the Asgardian façade slide away like so much oil and silk, expecting to see the disgust and shock and fear that always accompanies an accidental slip, but instead getting the sharp burn as Tony's fingers tighten on his thighs and his heart rate climbs as adrenaline and endorphins thrum through his body.
(Loki can see his pulse jumping in his neck in the glow from the arc reactor, and Tony stares at him like he wants to devour him and everything he is and Loki may have been alive for millenia but he doesn't know what to do with that)
"God," Tony says, and he sounds completely wrecked. "Why would you want to hide this?"
But Loki doesn't say anything as Tony manages to control himself enough not to fuck himself to completion right there and then, instead carefully moving one hand over the whorls and tracery of Loki's Jötunn skin as his hips thrust upwards in involuntary, infinitesimal movements.
"Why would you hide this," he says again, and then, "Oh, God, I want to kiss you," before pulling Loki down and pushing himself up so they meet in the middle, Tony's hand fisted in the hair at the base of Loki's skull and Loki's arms holding them upright as Tony pushes his tongue into Loki's mouth.
Tony's control slips sideways and he fists Loki's cock as he fucks into him properly, tug and twist as he digs his nails into the back of Loki's neck and scrabbles for purchase on his silk sheets.
Tony licks his hand with an expression so fucked-out he almost looks dazed, and then presses sloppy, open-mouthed kisses against every piece of Loki's skin that he can reach in an attempt to make him stay like that, real and perfect and just his in Tony's bed.
(because if Tony tastes of earth and mortality and life then Loki tastes of starlight and the ice that makes comets' tails and endless time that Tony wants to chase and own and keep, because Tony Stark has an addictive personality and he almost always gets what he wants)