One common theme is redemption. Bucky often has a past he's trying to move on from, and Sarah can be a part of that journey towards a better self.
Family is also a theme. Sometimes, their relationship is explored in the context of building a new family or fitting into an existing one. Bucky might find a sense of belonging with Sarah and her family, which is a really heartwarming aspect in many of these fanfictions.
Another theme is love against all odds. Given their different backgrounds and the challenges in the fictional universes they exist in, their love has to overcome many obstacles. For example, Bucky's past as a soldier and Sarah's own personal struggles in her life.
Overcoming obstacles is another theme. They might face things like social stigma due to Bucky's past, or external forces trying to tear them apart. But they always find a way to stay together and fight through it all.
One common theme is the exploration of their relationship against the backdrop of the complex Marvel universe. Since both characters have their own traumas and stories, fanfiction often delves into how they support each other through those.
One common theme is redemption. Bucky has a dark past as the Winter Soldier, and many fanfictions explore his journey towards redemption. For example, he might try to make up for the wrongs he has done.
A common theme is redemption. Bucky has a complex past, and many fanfictions focus on him trying to atone for his previous actions. Another theme is friendship. His relationships with other characters, like Steve, are often explored in terms of how they support and influence each other.
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.
One common theme is his struggle with his past as the Winter Soldier. His memories and the things he was forced to do often cause him a great deal of emotional pain.
One common theme is loyalty. Steve and Bucky have a deep loyalty to each other that is often explored. For example, in many fics, Bucky will go to great lengths to protect Steve and vice versa.
One common theme is the reaction of Bucky's friends and allies. They might be shocked at first, but then show support. For example, Steve could be there to help Bucky through the pregnancy journey.
Love and romance can also be a theme. Sometimes the OC and Bucky develop romantic feelings for each other. Additionally, adventure is a big theme, with the two characters going on various exciting missions or quests together.
One common theme is redemption. Bucky has a troubled past as the Winter Soldier, and in many fanfictions, Darcy helps him find his way back to a more positive self. For example, in some stories, she provides emotional support that aids his healing process.