Tony's the first to admit that he has something of an oral fixation; he makes no bones about it. He likes having things in his mouth, likes feeling them against his palate, rolling them with his tongue, discovering new textures and flavors. Or even revisiting known ones. Like now. Now is good. Now is fantastic even. Now he's giving Steve a blow job in the gym shower, on his knees on the hand-glazed tile.
He hums around his mouthful and it's sort of ridiculous how happy this makes him, like his personal road to nirvana is found through sucking Captain America's dick but then Steve makes that funny "hup"-ing sound he does before he comes and maybe, yeah, Tony could find enlightenment like this. He speeds up, chasing that vocalization, the only one he's ever known Steve to make during sex.
There's a few more of those delicious noises and then Steve comes silently, biting his lip and staring at Tony like he's solved an impossible equation. He probably has. Tony continues to kneel there, sucking gently on Steve's softening cock until he just holds it in his mouth. He's needy in a way he's shown to only a few, staying quiet with his eyes not leaving Steve's. He'll do whatever Steve asks, including nothing.
Steve's hand tightens in his hair and Jesus that's good, that's so good, no, why is Steve pulling him up and away? "Come here," he says, voice rough and low, with the kind of assured command that only the likes of Captain America can give. It does such things to Tony. "Hush," he says to the slide of one large hand up and down Tony and oh god his hands. So big and warm as it cups his ass and squeezes.
"You like it when I ta--mmph!" Tony shuts up then, but it's mostly because Steve has taken advantage of his open mouth to slide two fingers in. "Mmm!" Fingers aren't the same as Steve's dick, but they're better than nothing and alive with the taste of Steve's skin and cum still on his tongue
Steve rocks him up against his body, the hand on his rear setting a steady rhythm Tony gives in and follows. It's not long before he shivers and comes. Steve holds him through it. The hand that had cupped his ass slides up to caress his back again.
"Yeah. Thank you," he murmurs into Steve's neck.