One common theme is redemption. Bucky has a complex past and often in these fanfictions, Tony plays a part in his journey towards redemption or vice versa. For example, in many stories, they help each other deal with their own guilt.
Another theme is friendship. Despite their differences in the original storylines, in fanfiction, they often form an unlikely friendship. They learn to understand and support each other, like in the fanfic 'The Bridge Between Us' where they slowly break down the barriers between them.
Forgiveness is also a big theme. Tony has to forgive Bucky for things he did while under Hydra's control. And in reverse, Bucky has to forgive Tony for any harsh judgments or actions towards him. There's also the theme of teamwork. They are both strong characters, and when they work together, they can achieve great things, like saving the world or solving complex problems in the fanfiction stories.
Friendship is a very common theme. These three characters often form a strong bond in fanfiction, relying on each other for support, whether it's during battles or in dealing with personal issues. For example, in many stories, they help each other overcome their past traumas.
Friendship is also a big theme. Since they are all part of the Avengers universe, many fanfictions explore how their different personalities can form a strong bond. Tony's wit, Bruce's intelligence and Bucky's quiet strength combine in unique ways to create interesting friendship dynamics.
A prevalent theme is also sacrifice. Each of them is willing to sacrifice for the others in many fanfictions. It shows how deep their bond is. And the theme of trust is also there. They need to build and regain trust among themselves, especially given all the things that happen in the Marvel universe.
Another theme is redemption. Sometimes the fight is a way for Bucky to try and redeem himself in Tony's eyes. He might face Tony head - on in the fight, hoping that by taking the punishment or showing his remorse, he can be forgiven.
Another theme could be the support system around them. How their friends, like the Avengers, react and support them during this unusual situation is often explored. Also, the theme of facing the unknown together, as the mpreg situation is something not common in the normal world of the characters. They have to figure out how to deal with the physical and emotional changes that come with it.
One common theme is friendship. They are often shown building a strong bond despite their differences. Another is redemption, especially for Bucky considering his past. And teamwork is also a big theme as they are all part of the Avengers.
A common theme is friendship. Since they are all part of the Avengers, many fanfictions explore how they form strong bonds despite their differences. For example, in some stories, Bucky's past trauma is healed through the support of Bruce and Tony.
One common theme is redemption. Bucky has a complex past and Tony often has to come to terms with that. Another theme is friendship. They are two very different characters but in fanfic they often find common ground and become friends.
One common theme is the exploration of their complex relationship. Given their different backgrounds in the original stories, fanfiction often delves into how they bridge the gap between them. Another theme could be redemption, as both characters have had their share of difficult pasts.