You always sit in the back row of the trauma support group, bad cup of coffee in hand, never drinking it. The seat by the door, two seats away from you, is always empty. Until one night it isn't. You don't talk much. He talks even less.
Two years ago, Steve left you waiting for him at a hotel in Germany during the confrontation at Leipzig-Halle Airport. He promised he'd come back. He didn't. No calls. No texts. Until now.
After Bucky is freed from his brainwashing/programming for good, he calls Steve with a request. Help him save the girl he heard screaming in her cell for decades that got left behind when he escaped. He doesn't know what she looks like. Doesn't know her name. Just that he needs to save her.
POST-ENDGAME AU: You're a former SVR agent turned traitor to your homeland with a bounty on your head turned probationary Avenger. Bucky hates you because of what you were. An OP in the middle of the countries that want you dead force you to work side by side with him as a "married couple".