In comics, while Bucky has taken on the mantle of Captain America at certain points, it's not a permanent or default status. Steve Rogers is the original and most commonly associated Captain America.
Sure, Bucky has been Captain America in the comic universe. This happened after specific storylines and events that led to the passing of the mantle or under special circumstances.
It's popular because their relationship is so complex and deep. They have a long history together, from being childhood friends to facing all kinds of hardships. Fans love to explore the different aspects of their relationship, like loyalty, friendship, and the potential for something more. Also, the movies and comics give a great foundation for fanfiction writers to build on.
Well, I really like 'Shared Memories'. In this fanfic, it's all about Captain America and Bucky sharing memories that were long forgotten, which brings them closer than ever. Then there's 'A New Beginning' where they start a new life away from the chaos, building a relationship based on trust and love that they had in the past but lost along the way. 'Forgotten Promises' is also good as it unfolds the promises they made to each other long ago and how they are trying to fulfill them now.
A fanfiction could focus on an alternate universe where Bucky becomes Captain America instead. He has to deal with the same ideals but in his own unique way, while also having to face Steve Rogers in a different role, perhaps as an advisor or a reluctant ally. This would create a lot of interesting character dynamics.
In the comics, Bucky didn't become Captain America. Captain America has mainly been associated with Steve Rogers. However, Bucky has had significant storylines and developments of his own.
One great fanfic is 'The Long Road Home'. It delves deep into the relationship between Captain America and Bucky Barnes. It shows how Steve Rogers is determined to save Bucky from the clutches of Hydra. The story is full of action and emotional moments.
Well, 'Inseparable' is a fanfic that many like. It beautifully portrays the unbreakable bond between Captain America and Bucky. The story shows how they support each other during battles and in their personal struggles. 'Bucky's Redemption' is also a great read. It's about Bucky trying to atone for his actions as the Winter Soldier while Steve is right there by his side, guiding him. Then there's 'Cap and Bucky: The Lost Years' which explores what might have happened during the time they were apart.
There's also 'Bucky's Redemption in Steve's World'. This fanfic delves into Bucky's struggle with his past while Steve is constantly by his side, helping him heal. It shows their bond strengthening through various challenges they face in the modern setting.