Love against all odds is also a big theme. Given their different natures and the dangerous situations they are often in, their love story in fanfiction is often portrayed as something that has to overcome many obstacles. It makes for a very engaging and emotional read.
Another theme is redemption. Natasha might see helping Bruce control the Hulk as a way to redeem herself for her past actions. And Bruce might see Natasha as a chance at a normal life, which is a form of redemption for him. It's a complex interplay that is explored in a lot of the fanfictions.
One idea could be a story where Bruce and Natasha are on a mission together in a remote location. They have to rely on each other's skills to survive. Bruce uses his scientific knowledge to figure out a way to stop a dangerous experiment gone wrong while Natasha uses her combat skills to protect them from the threats around. Their relationship gradually deepens as they face challenges side by side.
In a fanfic, there could be a plot where Natasha is poisoned and the only antidote can be created by Bruce using his knowledge of biochemistry. But he has to do it while keeping the Hulk in check. As he races against time, Natasha's condition worsens. This creates a tense situation that tests their relationship and shows how much they mean to each other. They also share some tender moments during this difficult time.
The fanfiction 'Banner and Romanoff: Unlikely Allies' is also quite good. It starts with their professional relationship in the Avengers and then slowly evolves into something more. It has some really interesting character interactions and a well - paced plot that keeps you engaged.
One common theme is their relationship development. Since they both have complex personalities in the Marvel universe, fanfictions often explore how they get closer and understand each other better.
Redemption is also a big theme. Given her complex past, many fanfictions focus on her journey to become a better person. This could be through helping others, making up for past wrongs, or finding a new moral code to live by. Fanfics might show her working with charities or saving people in ways that she feels atone for her past actions.
One common theme is mentorship. Since Natasha is more experienced, she often takes on the role of guiding Spiderman in many fanfictions. Another theme is teamwork. They are both part of the Avengers, so stories often center around them working together to achieve a common goal.
A third common theme is personal growth. Both characters have their own traumas and pasts. When they meet, they often influence each other in a way that helps them grow. For instance, Naruto's positive outlook might help Natasha deal with her darker past, and Natasha's experience in a more complex and political world could make Naruto more aware of the bigger picture outside of his ninja village.
One common theme is the exploration of their complex relationship. Given their different personalities and backgrounds, fanfictions often dig into how they understand and complement each other. For example, Bruce's scientific mind and Natasha's spy skills make for an interesting dynamic.
In this type of fanfiction, themes related to trust are also common. The OC has to earn Natasha's trust, and vice versa. This can lead to some tense and interesting story arcs. Additionally, the theme of sacrifice can come into play. Either Natasha or the OC might be put in a position where they have to sacrifice something for the other's well - being.
One common theme is mentorship. Natasha, with her wealth of experience, often takes on a mentoring role for Peter. For example, she might teach him about stealth or how to better handle dangerous situations. Another theme is friendship. They come from different backgrounds, but through their shared experiences as superheroes, they form a strong bond of friendship. It's about two very different characters finding common ground.