Steve Rogers tried to change history so that Bucky Barnes could avoid the pain and torture he once suffered in Hydra. He ended up right back where he started, but his efforts were not in vain. He believes that he can always bring Bucky back in the end, and that strong and kind Bucky will not stay in the world that hurt him for too long.
CP includes Steve Rogers/Bucky Barnes, or Captain America/Winter Soldier, Captain America/Winter Soldier, Shield Winter, and various other titles. If the deputy CP must also include the science team (Bruce Banner/Tony Stark), I would not object. Otherwise, no other CP mentioned it.
Probably based on the Marvel world, mainly movies. However, if any setting is inconsistent with the entire Marvel universe, including various comics, animations and movies, please treat it as AU.
If the time did not catch up with the ending of "Captain America: The Winter Soldier", it was probably accidentally placed in some inexplicable parallel universe that I don't know where.
The idea comes from the Marvel animation "Ultimate Avengers". In this animation, Barnes did not fall off the train, but was still alive after the captain froze in the Arctic Ocean, got married and had children, and was already an octogenarian when he saw the captain again. But the story doesn't go that way.
Conception: