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.
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.
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.
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.
Often, the theme of trust is explored. Given their different personalities, building and maintaining trust can be a big part of the stories. Tony is more flamboyant and Bruce is more reserved, so how they come to trust each other completely is an interesting aspect. And of course, the theme of innovation, as they are both brilliant minds constantly coming up with new ideas.
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.
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.
One common theme is the power of their intellects combined. They are both brilliant minds, and fanfictions often explore how their ideas can create amazing things when they work together.