In fanfiction, Spider - Man could fit into the Fantastic Four by bringing in his own set of values. He has a strong sense of responsibility which could influence the group. Also, his intelligence in the field of science (he's no slouch in that department) could be an asset when the Fantastic Four are dealing with scientific problems. He might also introduce new ways of using their powers based on his own experiences in combat.
One common theme is teamwork. Since both Spider - Man and the Fantastic Four are superheroes, fanfictions often explore how they can combine their powers and skills to overcome challenges. For example, Spider - Man's web - slinging and acrobatics can be used in tandem with the Fantastic Four's unique abilities like Mr. Fantastic's stretching or the Invisible Woman's invisibility shields.
In fanfiction, if Spider - Man joins the Fantastic Four, there could be some really cool team - up scenarios. They might face new and more powerful villains together. For example, they could take on a super - intelligent alien that requires both Spider - Man's agility and the Fantastic Four's unique powers to defeat.
Obviously, Spider - Man himself is very popular. His quick - wittedness and acrobatic fighting style make him a fan favorite in any story. He can bring a sense of humor and energy to crossovers.
One interesting crossover could be Spider - Man and The Fantastic Four teaming up to fight a powerful new villain that neither could defeat alone. Maybe a villain with the ability to manipulate time and space, forcing them to combine their unique powers.
Perhaps Spider - Man would be initially distrusted by the Fantastic Four. He is a bit of a lone wolf compared to their more family - like dynamic. But then they would realize his good intentions and start to work together. For example, he could use his web - slinging to help Mr. Fantastic reach places during a rescue mission, while the Invisible Woman could provide cover for Spider - Man when he's outnumbered.
Another good one is 'Fantastic Four Meets Spider - Man: The Ultimate Team - Up'. It starts with Spider - Man getting a distress signal from the Baxter Building. When he arrives, he finds that the Fantastic Four are dealing with a powerful energy - based enemy. The story shows how Spider - Man's agility and quick thinking complement the Fantastic Four's more scientific and brute - force approaches to problem - solving.
One possible plot could be that Doctor Doom teams up with some of Spider - Man's villains like Green Goblin. The Fantastic Four and Spider - Man have to put aside their differences and work together. Spider - Man's agility and quick thinking combined with the Fantastic Four's unique powers would make for some great action scenes. For example, Spider - Man could swing in and save Sue Storm when she's in trouble, and in return, the Human Torch could help Spider - Man by burning away some of the webs that his enemies have trapped him in.
Sue Storm could be a great character to focus on. In a crossover, she could use her force fields in new and creative ways. Maybe she has to protect Spider - Man from some of his more dangerous enemies when he's outnumbered. Also, her relationship with Reed Richards could be explored further in the context of a crossover. How would she react to Spider - Man's more impulsive nature? And how would she use her powers to help Spider - Man and the Fantastic Four work together more effectively? There are a lot of interesting storylines that could be developed around her.
The Thing might be the one. He has a bit of a short temper sometimes. If Spider - Man accidentally gets in his way or says something that rubs him the wrong way, he could start a conflict.