Clint Barton, aka Hawkeye, doesn't know where his wings came from. He hasn't a clue, and he's not entirely sure he wants to learn. He kept them hidden in the past, before SHEILD; in his line of work, the less noticeable you are, the longer you survive. His black arrows, always straight through the heart, kept his reputation high enough. And although his arrows and bow kept him hidden in a veil of fear, enormous wings would work for him in a more... negative... fashion. Even when Coulson pulled him in to SHEILD, few knew about them, and those few only by accident.
Coulson wondered why Clint refused to take off his shirt in front of others. In a ship full of men, it was a common occurrence to see soldiers walking around half-nude. He always pulled one of his disappearing acts whenever he needed to change, especially in the locker room with other recruits. When others decided to hold a quick game of skin vs. shirts basketball, he always managed to worm himself onto the shirts side. Even swimming, he wore a loose t-shirt.
It wasn't until a dangerous mission gone awry that Coulson saw a shirtless Clint. It was just the two of them, alone somewhere in the snowy alps. Clint, out on reconnaissance, had been ambushed unexpectedly and a shot grazed his side while rocks, knives, and tree limbs scraped and clawed at his back. The heavily bleeding agent had stumbled back through the snow to the safe house, where he promptly passed out on the doorstep.
Coulson had managed to drag him onto the table, taking care of the bullet crease on his side before turning over his still unconscious operative. There, among the numerous cuts and bruises, he uncovered something he'd never expected to see. A pair of tightly folded, feathery bundles sat snugly in the curves of Hawkeye's back. Vowing to ask his agent what the hell was going on as soon as he regained consciousness, Coulson patched up Clint's back, finishing just as the man woke up.
Clint jerks back into awareness, instantly grabbing for a shirt, but freezing when he sees Coulson's face. It's too late to keep his secret from his handler any longer. Without a word, he stretches his back and opens his wings.
They are incredibly large when he extends them, wingtips gently brushing the wooden walls of the small cabin, easily a good seven meters across. Strong muscles do incredibly delicate work, simultaneously extending while carefully pulling every feather into its correct position. The low light of the cabin glimmers off Clint's feathers, turning meters of muscles and bone into a wall of shimmering gold. Streaks of black weave their way into the shinning tips.
Coulson reached out a cautious hand to touch them, even as Clint flinched back. But Coulson didn't stop, and his hawk let him touch his wings. Coulson marveled at the waterfall of gold, his fingers catching on the occasional scar. Clint marveled at the realization that his wings could feel soothing, and not just pain.
After that, neither man spoke aloud about the hawk's secret. Life was as it had been before. But every year, on one particular day in May, Coulson would borrow a Quinjet, and would fly to a field in Iowa, in the dark, and Clint would fly. And Coulson never wished he was in the sky with him, because the sky was his hawk's, and his was content to let him soar.
A gift for a friend of many colours, for whom this was long in the making. May you have a happy holiday. –Author 2