Clint Barton has Natasha Romanoff etched delicately down his spine. In the days before Barney turns mean he'll say to him that the name sounds Russian. When they join the circus they both joke that this must be how he'll meet her. Perhaps she'll be a sword swallower or contortionist, train the dancing bears or walk the tight rope. Whatever it is that happens at the Russian circus. A fourteen year old Barney tells him knowingly that all Russian girls are practically acrobats and can throw knives.
He catches the sword master stealing money and does the right thing. His brother turns on him and Clint won't stay and be beaten, now that he's old enough to run. He ends up working for the mob, killing who the boss tells him to. He wouldn't be surprised to meet a Russian girl in those circles but he doesn't really want to. He wants a nice girl, one who doesn't work for the mob.
He joins SHIELD and works his way up. He's the best they have and they send him to kill the best there is. Her name is the black widow and she is not a ghost. She is the person in the background, the pretty but forgettable girl on the arm of someone later found dead. He has the arrow knocked, pointing right to her heart. She knows it. She could fight back, could probably even win. She doesn't. He asks if she wants to live. She hesitates.
For the first few days she doesn't tell him her name, doesn't say one word to him. He tells her his name and she stares at him with a calculating gaze. He gets use to cold glances and interested looks. He's just glad that she hasn't tried to kill him in his sleep. He takes her back to headquarters and argues with Coulson and Fury over her. He wins. Her paperwork says Natasha Romanoff and she checks no nationality.
Natasha is born with Clinton Barton stamped on the curve of her back. Her teachers at the red room remind the girls of their duty. If you find them, kill them. She is nineteen when she meets the winter soldier. She is one of the few to know his name is James, but she never uses it, unless they're alone together. They put them alone in a room, at least once a week, trying to create a new race of killers. At first they simply did what they were told, but as Natasha climbed the ranks she made the request: more time with him. They would sit in the room and talk sometimes. It was enough. The young girl killer fell in love with the ghost in the night. They caught on and ripped him away from her, ceasing the unsuccessful experiments. She is cold and says that she doesn't care. This is what they want to hear. She burns the place down a few weeks later.
The winter soldier is sent to kill her. They have wiped her from their memory. Him remembering Steve would not be the first time they didn't do as good of a job as they thought, however. He makes his hands miss. She runs.
Clint Barton tells her his name and she questions why this seemingly good man would be her soul mate. She could understand if it was James. The controlled killers. But not the kind archer who makes her waffles and the monster with red in her ledger. They never say anything about the names on their backs. Budapest changes that.
They are paired together for that mission. When the mission is complete they sit on the highest roof they could climb to, which between the two of them is pretty high. "You know, my brother use to say that your name sounded Russian. But why is it in English?" Clint asks casually. "The names on our backs are not the names we are born with. They are our soul mates true name. Maybe I was Russian once. But I am not now."
They kiss that night, giving in to the prickling words.