One common theme is the exploration of their relationship. Given their different backgrounds - Steve from the 40s and Natasha being a trained assassin - how they come to understand and trust each other is often explored.
One plot idea could be a mission where Black Widow and Steve Rogers are undercover as a couple in a high - society event. They have to gather intel while also dealing with their growing, unspoken feelings for each other. Another could be a story set in an alternate universe where they are the last two Avengers left and have to rely solely on each other to save the world. Or perhaps a story where they are training new recruits together and start to see each other in a new light as they share their different combat experiences.
One popular 'Black Widow Steve Rogers fanfic' is 'Shield and Daggers'. It has an interesting plot where they team up for a secret mission and their relationship slowly develops in the midst of danger.
Love and support are very common themes. Steve is often depicted as being extremely supportive of the OC during her pregnancy, showing his caring and protective nature.
In 'Steve Rogers wife OC fanfic', a frequent theme is the power of love. Love gives the OC the strength to deal with the difficulties of being with Steve, like the public attention and the dangerous situations. Another theme is cultural clash. Since Steve is from a different era, there can be differences in values and beliefs between him and the OC, which makes for an interesting exploration in the fic. And the theme of friendship also often shows up, as the OC forms friendships with the other Avengers while being in a relationship with Steve.
Steve Rogers is the paragon of virtue, always following his moral compass. In a fanfic, his steadfastness can be contrasted with Black Widow's more morally grey past. For example, when they face a decision about whether to spare a villain who has information but has also caused great harm. Steve would be inclined to uphold the law and do the 'right' thing, while Black Widow might consider more practical, if not entirely ethical, solutions. This can create tension and also show how they grow to understand and respect each other's viewpoints.
Another theme is the struggle between duty and personal feelings. They both have important jobs, and often in these fanfics, they have to figure out how to balance their growing relationship with their responsibilities. For example, in some stories, a big mission might put their relationship to the test.
One common theme is loyalty. Their loyalty to each other is a big part of their relationship and is often explored in fanfics. For example, Bucky always being there for Steve, and Steve never giving up on Bucky.
Survival is also a common theme. Given her dangerous life, fanfics often show how she manages to survive in difficult situations. Her identity is another theme. Writers like to play with the idea of her true identity, whether it's the Natasha Romanoff we know or if there's more to her. And loyalty, whether it's to her friends, her cause, or her own sense of right and wrong.
One common theme is love and attraction. Often, the female characters in these fanfictions are attracted to Steve Rogers' noble and heroic qualities. For example, in many stories, a female character might fall in love with Steve as she sees his selfless acts of saving others.
One common theme could be the challenges Steve Rogers faces while dealing with the pregnancy, considering his role as a superhero. Another might be the relationship dynamics between him and the other characters during this time.