I really like 'Partners in Science'. In this fanfiction, Peter and Bruce start working together after Peter discovers some strange radiation that he can't figure out on his own. Bruce helps him analyze it, and their friendship grows throughout the story. It has some really cool action scenes where they have to fight off bad guys who are also interested in the radiation.
Another theme is the exploration of their dual identities. Peter has to balance his life as a student and Spider - Man, and Bruce has his own struggles with the Hulk. Fanfictions often explore how they can relate to each other's problems and support one another in dealing with their identities.
Perhaps they would team up to fight a common enemy. Peter's agility and combat skills combined with Bruce's Hulk - like strength could make for a formidable duo. They could be facing a villain who is both a scientific threat and a physical menace.
One common theme is mentorship. Bruce could be a mentor to Peter, guiding him with his scientific knowledge. For example, in some fics, Bruce helps Peter with his web - shooter technology.
If Peter is Banner's son in fanfiction, there could be a great deal of scientific exploration between them. Peter could learn a whole new level of science from Banner, and they could collaborate on projects. This would enhance Peter's intelligence even more. Also, Peter might struggle with the idea of being related to the Hulk. He'd have to deal with the public perception of his father and how that affects him as Spider - Man.
Their first meeting could be a bit awkward. Peter might be a bit star - struck seeing Bruce, and Bruce could be initially cautious around this young, super - powered kid. Maybe Peter accidentally stumbles into Bruce's lab while looking for something related to his own science project.
In fanfiction, anything can happen. Maybe there was some sort of scientific experiment gone wrong or a strange twist of fate. For example, perhaps Banner's DNA was somehow mixed with that of Peter's parents during a top - secret project. This could lead to Peter being biologically related to Banner in the fanfiction universe.
Well, FanFiction.net is also a great place. There are many different takes on the relationship between Bruce Banner and Peter Parker in the fanfictions there. You might have to dig a bit through the search results, but it's worth it.
It could be a mad scientist who is jealous of Bruce's work with gamma radiation and wants to create a similar but more dangerous form of it. This new radiation form accidentally makes Peter sick when he gets in the way during one of the villain's experiments.
One possible plotline could be that Peter Parker gets sick with a mysterious illness that even his enhanced healing can't quickly fix. Dr. Bruce Banner, with his scientific expertise, tries to find a cure. Along the way, they bond over their shared experiences of being different and having to deal with the consequences of their powers.
One great 'Peter Parker and Lorna' fanfiction is 'The Meeting of Two Worlds'. It beautifully weaves their different universes together and shows how their powers could interact in unique ways. The story has a great plot that keeps you hooked from the start.