Author's Note: I got an anonymous ask for Soulmate Stucky, so of course I botched the AU part and was just a big dork writing about dumb kids from Brooklyn.
Bucky Barnes learned about soulmates when he was six years old, sitting at his father's knee and asking how it was possible to know for certain that you were destined to be with someone. He was romantic and had a silly heart, even back then. Stories flowed like water in their house, and he memorized the poetry used to recount the first time his parents' eyes met; how his father described the sound of her voice when he finally heard it; his mother's soft sigh as she recalled the electric excitement of his hand in hers.
Everyone always said that you would know your soulmate the moment you met them. It's different for everyone, details standing out to each person based on chemistry and personality and the mysticism inherent to all discussions of souls. They said it wasn't a science, not like the architecture and feats of engineering that caught his rapt attention. Everyone just knows, somehow, intrinsically, that that person is your destiny, their soul calling out to yours. That person is your most something.
Mr. Barnes described it as tunnel vision, because he only had eyes for the woman he would marry. She filled rooms and thoughts until there was nothing else and he had sworn he would drown in grief if she didn't accept his proposal. Mrs. Barnes said it was like seeing beauty for the first time, like gazing upon a sunrise after a lifetime of darkness. Soulbonding, they explained when he turned eight, transcended the kind of love or respect or admiration that he was familiar with. It was unbreakable, inescapable. It was the most instinctual of emotional responses.
Bucky Barnes is eleven years old when it happens. There's a pressure in his chest like his heart is being squeezed too tight and he finds himself turning down streets he doesn't know, dragging his feet and peering into dirty alleyways. He stumbles upon his soulmate in the middle of a fight that he's losing, but the scrawny kid keeps getting up, knuckles and nose bloody.
The boy is beautiful, but it is not his most striking feature, not the thing that stays with Bucky for days afterward. What he notices most is the way the boy sways on unsteady feet, the stubborn jut of his jaw, the defiant gleam in his eyes. What he will remember most about this day is knowing that he can never let this boy go, that he will shatter bones and destroy dreams for this boy to keep him safe.
That, of course, is precisely when the stupid punk opens his big mouth again and gets dropped by a sloppy left hook from one of the three opponents he has gathered.
It is his first fight, but protecting the scrawny boy comes naturally. His fingers curl into fists on their own accord, swing out with force to find their mark. One of the other boys gets him in the mouth, splitting his lower lip. He ducks under one's reach to slam into the chest of another. His elbow finds a solar plexus, his knee drives hard into someone's gut. He blackens eyes and breaks noses. Someone spits out a tooth as they leave. Bucky's hands ache when he is done hitting.
"Thanks," Bucky's soulmate says breathlessly, and the smile Bucky has paid for in blood is lopsided and perfect. The boy's eyes are big and blue and wet. He thinks he could stare into them for days and not get bored, just lost, so wonderfully lost in this person. If he had this boy, he wouldn't need water or food or air; he could survive on this smile and this look and this moment for the rest of his life.
This is his soulmate, looking up at him in a dirty alley with red smeared across their faces and their hands. His father said his soulmate had the most alluring voice of any woman. His mother said her soulmate was the most handsome man she'd ever known. He thinks this boy, this beautiful boy -
"But I didn't need your help."
"Huh?" Bucky sputters ineloquently, mouth gaping in disbelief.
"Ya oughta mind your own business. M'not a little kid, an' I don't need nobody takin' care of me."
It rubs him wrong because that's exactly what Bucky plans to do. He's going to keep this boy close and take care of him and look after him and let no harm ever come to him again. And of course that's the one thing this boy doesn't want. Of course it is. Bucky frowns, a deeply serious expression that sits oddly on his young features.
"Yeah?" Bucky says when he finally manages to find his voice again. "I heard that before."
"What do you know?" the boy snaps back, eyes narrowed into a glare.
"More'n you, dummy!" he retorts, and the boy brings his fists up like he's jonesing for another fight. Bucky sighs, rolls his eyes, and throws his arms up. His fingers interlock behind his head, palms still hot from the brawl when he places them on the back of his neck, rocks on his heels, and pouts at the boy. "M'not gonna fight you. You probably like gettin' into fights."
It makes the boy laugh. Bucky thinks he will end up dreaming of that sound until his end of days.
"Yeah, maybe," the boy says, and lowers his fists. "Name's Steve."
"Bucky," and he drops the hold on his neck to toss an arm around Steve's bony shoulders, pulling him in close against his ribs. "What am I gonna do with you, huh, Stevie?"
"Why you gotta?" Steve asks, suspicious anger back in force as he tries to shake Bucky's arm off.
Bucky snorts. He has to do something with Steve because if he doesn't, Bucky's pretty sure the little smartass is gonna get his teeth kicked in or his skull cracked open on the pavement somewhere. He looks both ways down the deserted alley before tucking his head to press his mouth to Steve's sweat-dampened forehead.
"Because," Bucky answers fiercely, holding Steve's gaze. The boy is blushing hard, from his hairline down past his stretched out collar, ears burning pink. "I'm gonna be your best friend, as of right now."
"Says who?"
"Me. Who's gonna stop me? You? Yeah, right."
"Who'd wanna be friends with a jerk like you, anyway?" Steve asks, looking anywhere but Bucky's face and smirking mouth. Bucky Barnes knows this is his soulmate, not because Steve is the most beautiful boy or, as he learns later, the kindest boy, the sweetest boy with the best heart. It is not the purity of this boy's soul that calls to him. He knows this mouthy, stupid little punk is his soulmate because Steve is, hands down, the most annoying little shit in Brooklyn.
Well, everyone always said his soulmate would be his most something.