Perhaps in a fanfiction, Bruce Banner discovers a new form of science that can enhance Thor's powers even more. Thor, in turn, helps Bruce understand the Asgardian view of the universe, which gives Bruce new insights into his own work. This could lead to a series of events where they team up against a common enemy that is a threat to both Earth and Asgard.
Perhaps Bruce Banner adopts Harry Potter after the events at Hogwarts. He takes Harry to the world of science, showing him things like advanced laboratories and scientific research. Harry, in turn, shows Bruce the wonders of magic. Their bond grows as they learn from each other, and together they face new threats that combine elements of both the magical and scientific worlds.
Another fanfiction could focus on their friendship. For example, they could have a weekend getaway where they just relax and talk about non - work - related things. They might share stories from their past, like Tony's wild college days and Bruce's early research experiences. It would be a chance to explore their characters on a more personal level.
Another plot twist might be that Thor loses his powers and Bruce, in an unexpected turn, uses his scientific knowledge to transfer some of the Hulk's power to Thor. But this comes with a price, as Thor now has to battle with some of the Hulk's uncontrollable rage. This forces them to work even closer together to find a solution.
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.
Another fanfic concept could involve Harry Potter somehow ending up in Bruce Banner's world. He might be there to learn about modern Muggle technology and end up meeting Bruce. Together, they could face a threat that requires both magic and scientific knowledge to defeat. For example, a villain who is using both dark magic and advanced technology to cause chaos.
In fanfiction, Bruce is often portrayed as the brains behind many of the Avengers' strategies. His scientific knowledge is invaluable. At the same time, his struggle with the Hulk can be a source of both drama and humor. For instance, there might be scenes where he accidentally turns into the Hulk at the wrong moment, creating chaos but also a chance for him to show his strength.
Another plot could be that Bruce Banner is doing some research on a new form of energy and it somehow links to Harry's magic. Harry is brought in to help understand this strange new energy which has properties similar to magic. In the process, they learn from each other's worlds and develop a friendship while trying to keep this discovery from falling into the wrong hands.
One idea could be that your OC is a therapist hired by the Avengers to help Bruce Banner deal with his psychological issues related to the Hulk. This would involve deep emotional conversations between the two characters and a new perspective on Banner's struggle.
One possible title could be 'The Iron and the Hulk: A Stark - Banner Alliance'.
Loki may also kidnap Bruce Banner as a way to get at the Avengers. Since Banner is an important part of the team, taking him hostage could be a strategic move to draw out the other Avengers and then manipulate or defeat them. It could be part of a bigger scheme to gain power or control over Earth or the universe.