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.
Perhaps there could be a story where Harry and Bruce Banner meet in a multiverse - type situation. They are both the only ones who can stop an evil force that is spreading across different universes. Bruce uses his scientific knowledge and Hulk's strength, while Harry uses his magic skills to fight this common enemy. They have to overcome their differences in how they approach problems and learn to work together effectively.
Maybe Fem Harry Potter is on a quest to find a magical object that has found its way into the Marvel world. Bruce Banner, in his Hulk form, initially scares her but then they realize they can help each other. The Hulk's strength could be useful in protecting Harry from physical threats while she uses her magic to protect Banner from magical ones.
One idea could be that Bruce Banner is somehow transported to the wizarding world of Harry Potter. Maybe he arrives during a time of great danger, like when Voldemort is at his most powerful. Bruce's scientific knowledge could be combined with magic in unexpected ways. For example, his understanding of gamma radiation might interact with some of the more dangerous magical spells or potions. He could also form an unlikely friendship with Harry Potter. Harry could teach him about magic, while Bruce could show Harry some of the scientific concepts from his world.
One plot idea could be Percy and Bruce Banner teaming up to fight a new type of monster that is affected by both magic and gamma radiation. Another could be Percy getting lost in a scientific research facility where Bruce works and they have to figure out how to get Percy back to his world while also dealing with some lab - created threats. Maybe they also discover that there is a connection between the Greek gods and the science behind the Hulk.
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.
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.
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.
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.
Some fanfics might focus on their relationship in the past. Maybe exploring how they first met and fell in love. It could also involve dealing with the secrecy and danger that Bruce's condition brought to their relationship, like how they had to hide from the military or other threats.
One possible plot could be that they are brought together to solve a mystery that combines magic and science. Maybe a powerful artifact has been found that is both magically and scientifically complex, and their combined knowledge is needed to figure out how to handle it safely.
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.