A/N: I would really love to see BuckyNat in the MCU, so I wanted to explore how that might work. First half is their relationship in Russia, and the second half is some time after Bucky and Steve have been reunited and Bucky is hanging out in Avenger's Tower. It could be post any of my other stories, or stand alone :) I hope you enjoy it! Titles from "Functional" by Imperative Reaction.

Part 1: The Widow and the Winter

1. We are functional, we are efficient

He is surrounded by cold and metal. His hand is reaching out toward the tiny window in front of his face. In a moment, he can move his arm and lowers it to his side tentatively. As the cold recedes further, he clenches his fingers into fists and rolls his shoulders, shaking his head to shed the thin layer of ice covering his body. The door before him opens at last and he steps out tentatively, more shards of ice dislodging and falling to the concrete outside of the chamber.

The room in which he stands is twenty feet in length and thirty feet long. In addition to the chamber he just stepped out of, which is located in the right corner, there is a metal chair surrounded by technological equipment settled against the wall to the right and a gurney framed by medical supplies on the left. Before him is a blank wall with a door on the far left.

The room also contains three people: two men in shirts with their sleeves rolled up and a man wearing a lab coat over a suit. One of those in shirtsleeves is standing before the monitors; he is five ten, one hundred sixty pounds, age late thirties, no apparent combat skills: not a threat. Another is standing closer, to the right of him, looking at readings on a monitor; five eight, one hundred forty pounds, early forties, close proximity but no apparent combat skills: not a threat. The third is facing him, standing roughly five yards away; late forties, five eleven, one hundred eighty pounds, authoritative, some military training: potential threat.

"How is he?" the potential threat asks.

"Stable. Readings are at normal levels. He should be able to accept mission parameters in the next few minutes," the closest nonthreat answers.

"Good. Inspect the wounds," the potential threat tells the other nonthreat.

His muscles tighten as the man leaves his place by the chair and approaches where he stands, pushing his sleeves further up. The man walks around him slowly, pausing to inspect an area on his shoulder. His skin feels tight there; it is likely healing from some injury. He doesn't remember anything about that. Inspection completed, the man steps away.

"The healing process is very advanced, sir, but not quite complete."

"He was awakened too soon?"

"Not necessarily, sir. The process is different when he is in cryofreeze. We haven't been able to work out all the variables at this time."

"Fine. How about the arm?"

"Updates have been installed and it should be functioning normally."

"Should?"

The man in his shirtsleeves looks surprised, glancing toward his fellow, then back at the man to whom he's been reporting. Then all the eyes in the room turn to him expectantly. "Lift your left arm," he says.

He frowns uncertainly. "Soldier, demonstrate the capabilities of the prosthesis prototype," the senior officer orders.

Obediently, he lifts his left arm and twists it, tightening his fingers into a fist, then spreading them back out. The movement is accompanied by a soft whirring and muffled sound of gears turning beneath the smooth metal plates. The men nod at each other, satisfied.

"Status report."

He glances between the three of them briefly before answering. "Codename: the Winter Soldier. Status: mission ready."

"Excellent!" The man in charge smiles at him. "There is a woman called Katya Durova. She has betrayed us and will share our most important secrets with our enemies. If our great nation is to survive, you must find her and take her down. Do you understand?"

"Yes."

"You will be briefed on her location and the best strategy to reach her in time. These men will help you get ready. You will need to hurry, Soldier," the man in the lab coat tells him as he turns and walks out the door.

He stands silently at the men approach hesitantly. When he doesn't react, they dress him in his mission gear, consisting of leather armor and an array of weaponry: two pistols strapped to his hip, a semi-automatic strapped to his back, a few grenades on his belt, and more ammunition in his pockets. The technicians, as they seem to be, gather these items from a duffel bag one of them fetched from outside the door. The other one tests his arm again before he is deemed ready.

He walks out of the door and down the hall to the left. The second door is open and he walks into it. There is a large table in the center of the room, surrounded by chairs, and otherwise empty. He enters and stands against the wall to wait. After a small period of time, the senior officer comes in, flanked by two junior officers. These latter are both in their twenties, one hundred and eighty pounds, five foot ten, have had combat training, and are more of a threat than anyone he has encountered so far.

Listening carefully, he assesses the intelligence they are able to provide and determines how best to approach the situation. When the brief is finished, he agrees to the mission and outlines his ideas on how to complete it. The man in charge smiles again, nodding in agreement. Then he is escorted out of the room and down the hall to the door passed the one where he was awoken. Inside, there are several vehicles waiting to transport him and his backup team to the specified location.

"Our enemies are going to try to extract her. We can't allow them to dishonor our country that way. If they are foolish enough to try when you make your attack, make sure they regret it," the senior officer tells him before he climbs into the truck.

"Yes, sir," he replies quietly.

He will ride beside the driver. A rifle is handed to him and he inspects it carefully. They drive. It will take them roughly two hours to reach their destination. There is no one else in the vehicle with him and the driver. The team uses its own vehicles, and he is aware that they do not like being in a contained space with him. That is an accurate assessment on their part, he thinks. He leans back against the headrest of the chair and closes his eyes.

The target is in the city. He knows the roads through it; he has often been here on missions. Its name is unknown to him, irrelevant. Names often are, he has found. Their truck is military-grade, but there are many others just like it here. It won't attract unwanted attention. They pull up and stop next to a night club. He climbs out, pulling the rifle over his shoulder, and walks to the doors of the club.

Durova feels she might be safe if she is in a crowd. Those extracting her will agree. There are few other options in her immediate vicinity that will satisfy what this place will. The men at the door look at him in shock as he approaches, belatedly reaching for the weapons on their waists. When they fire, he catches the bullets on his left arm and they bounce away, having done minimal damage. The men panic when they see this and he steps forward quickly to strike them both with his metal fist. They crumple to the ground, possibly dead, possibly unconscious. Threat neutralized.

He pulls the door open and peers into the dark interior. Lights flash everywhere and music is blaring. There are roughly three hundred people in the main area, the dance floor a fifty by fifty foot square. He briefly scans the crowd for Durova. She is not hard to find; no one else looks at his intrusion in the room with quite as much terror. Others are concerned, annoyed, disturbed, but she is terrified. She knows who he is. When she sees him looking at her, she ducks to the floor, moving toward the back. There is an exit in that direction. She won't reach it. He jumps onto a table nearby, glass crunching under his feet, a few screams reacting to the movement. Lifting his rifle, he is lining up his shot when bullets bury themselves in the wall behind him.

Screaming and shouting fills the room, louder even than the music, which continues to play. He drops back to the ground and tosses the table on its side in front of him, using it for cover. Glancing up briefly, he identifies the shooter and waits a moment while more bullets fly through the air. The aim is not precise, but unlikely to be coming from a civilian. Her extraction team may have arrived. He lifts himself just enough to snipe the man who was shooting at him. When no further weapons are shot in his direction, he stands and kicks the table forward, clearing a path to the target, who has not yet reached the door. She screams.

The exit door opens and the barrel of a gun is pushed through, aiming haphazardly at him. He tosses a grenade through the opening and there are shouts from inside for a moment before it goes off. If that was her extraction team, they were woefully under trained. Distractions eliminated, he trains his rifle on Durova and eliminates her, too. Then he turns and walks out the way he came, the club patrons staring, silent, after him.