Well, in the Avengers series, Hulk and Black Widow did share a connection. Black Widow was one of the few people who could approach Hulk when he was in his angry state. She had a certain influence on him. It wasn't exactly a traditional love story, but there was definitely an emotional bond between them. For example, in some scenes, you could see the way they interacted, which was different from their relationships with other characters.
One interesting fanfiction could be about Black Widow and Hulk having to team up for a secret mission. In this story, Black Widow uses her intelligence and combat skills to help Hulk control his rage during the mission, and they develop a deeper understanding of each other.
In many fanfictions, there is also an undertone of a deeper emotional connection. Since Black Widow was one of the few who could somewhat calm Hulk down, it's not uncommon to see a relationship that goes beyond just friendship. For example, Black Widow might be the one person Hulk trusts completely, and she might have a special place in her heart for him as she sees the good in both Banner and Hulk.
Archive of Our Own (AO3) is a great place to find avengers black widow and hulk fanfiction. It has a wide variety of stories, from action - packed adventures to more emotional and relationship - focused ones. The tagging system on AO3 makes it easy to search for exactly what you're looking for.
Another storyline could be set in a post - apocalyptic world where only Hulk and Black Widow remain of the Avengers. They have to survive together against new threats. They build a relationship as they fight to protect what's left of the world. Black Widow uses her combat skills to scavenge for resources while Hulk defends their territory from any attackers.
A significant moment was when Black Widow went to find Hulk after he had disappeared. It showed that she cared about him. Also, in some group scenes, the way they looked at each other or reacted to each other's presence was telling. For instance, when Hulk saved Black Widow from danger, it was a moment that emphasized their connection. Their relationship was built on trust and a kind of mutual reliance within the context of the Avengers team.
Sure, there are pieces of fanfiction focusing on a Hulk - Black Widow romance. In these stories, the writers usually play with the idea of the contrast between the Hulk's brute strength and Black Widow's agility and intelligence. It could be a story where the Hulk protects Black Widow in a new and unexpected way, leading to feelings developing between them. They might also explore how their different backgrounds in the Marvel universe could bring an interesting dynamic to a romantic relationship.
Another theme is the power of friendship. They come from very different backgrounds, but in fanfiction, they often form a strong bond. They support each other in battles and in personal growth. Like when Black Widow is in a tough situation and the Hulk comes to her rescue, showing that they have each other's backs.
Another theme is redemption. Sometimes the Hulk is portrayed as a character seeking redemption for the destruction he's caused, and Black Widow helps him on that journey. It's about how they can find a new purpose together. A lot of fanfictions also play with the idea of them being outsiders in the Avengers group, and how they form a special bond because of that.