Sambucky au where both Bucky AND Sam got captured by Hydra and turned into assets.
Bucky has the same backstory—friends with Steve, fell off the train, got captured, and is the Winter Soldier.
Sam has a few differences (obviously). He got into the Exo7 program, then Riley dies. But instead of leaving the program, he continues—something about his promise to Riley to become the greatest pararescue. Unfortunately, one day his wingpack exploded (either planned by Hydra or just an unfortunate accident) and his body was never found, he was declared MIA. Surprise, surprise, Hydra took him.
Hydra wasn't very kind to him as they were to Soldat (which is already bad). They experimented on him, adding metal wings to his back that are connected to his bones. The metal wings are large, larger than his body. Its ends are sharp—so sharp it can slice through human bones, and they gave him something that's shaped like a bird's talon. They gave him a mask similar to the Soldat's and a pair of red goggles that allow him to see farther than a normal human can, hell his eyesight is greater than Soldat's, who is a super soldier.
After they "fixed" Sam Red Falcon, they placed him under Soldat's care, basically making the latter a handler to Red Falcon. When they both met, they were attached to each other instantly.
At first, Soldat was unsure about this decision. How could a machine like him take care of others? But when he met Red Falcon, he could feel his heart getting lighter even if they had little conversation for reasons he doesn't know. It helps that Red Falcon didn't question or eye at his metal arm like the others do. And when they get assigned to a mission together? The way they fought could be called a dance with how in sync they were.
Unfortunately, their time together is short because after each mission, Red Falcon is separated from Soldat to avoid attachment (which failed because they already are, but Hydra doesn't need to know that) and can see him only when they have a mission together.
They were content like this, meeting each other, going on missions, and very rarely, show affection to one another when they're sure Hydra isn't watching their every move.
It all went to hell when a blonde man appeared.