The truth is, I never looked at him as a sidekick. I didn’t want to play him as a sidekick. I didn’t want that informing my performance. I just wanted him too…Look, for me, Bucky lives in his own world. Steve is his family back home. When Bucky goes to war, that is what he is doing. He never wants Steve to go to war. He doesn’t want Steve to be in a position where he can get hurt. He doesn’t ever want to lose Steve. That is the only family he’s got.
But Bucky lives in his own world, at the same time. He travels the world. He has been around. He has seen things. When he comes back, what I think happens, when they both go on their mission, this is where the quote-unquote sidekick thing kicks in. When Bucky comes back, the next time Bucky sees Steve, Steve is a different man. Not a person. But an entirely different man. That changes everything, including the dynamic of his relationship. Bucky has to follow Steve into battle, because it never changes for him. That he will always have to look out for his brother. You know what I mean? There were aspects of that, that we’ve seen in other films before. Where brothers stand up for each other. One goes to war, because he doesn’t want anything to happen to the other guy.
There are different moral reasons at play here, other than, “Hey, we’re going to go be super heroes. I think the world in the comic books looks at this as something that will take care of itself. But for me, I am interested in keeping it all about the reality of their relationship. The connection between people, and why Bucky does what he does."