Well, it could be a story where they team up to fight a common enemy. Maybe a villain who has the ability to manipulate time or something. Spiderman could use his intelligence to come up with a plan, and The Flash could quickly execute it with his speed. They would learn from each other's strengths and weaknesses along the way. For example, Spiderman could teach The Flash about using the environment to his advantage, while The Flash could show Spiderman how to move even faster in a fight.
It's hard to say. The Flash has his incredible speed, which gives him an edge in terms of mobility and quick attacks. But Spiderman is extremely agile and has his spider - sense, which can help him anticipate The Flash's moves. So neither would be completely dominant.
Well, it can show different versions through the eyes of the fan. For example, a fanfiction could have a version of Spiderman who has a different suit, like one made entirely of nanotechnology that can transform into different shapes. The encounter between the real Spiderman and this fan - created version could explore how different looks can affect the perception of the hero.
Perhaps in the fanfiction, a young Spiderman fan who has a special power he doesn't know about yet meets the real Spiderman. They both have to figure out how to use the fan's power to stop a group of criminals who are stealing tech from Oscorp. This would involve a lot of character development for the fan character as he discovers his abilities with Spiderman's guidance.
Another possibility is that a character from Glee, say Rachel Berry, discovers she has some sort of meta - human ability similar to the Flash. The Flash has to come and train her to control it while also dealing with the chaos that her new powers cause within the glee club dynamic.
It could be Doctor Octopus. He might have some new, more dangerous tentacle - like devices. He decides to target both Spiderman and female Spiderman because he views them as obstacles to his scientific experiments and his desire for power. He kidnaps some innocent people to lure them into his traps and tries to defeat them in a fight.
In this fanfiction, the female Spiderman could be a huge fan of the original Spiderman. She has been following his adventures from afar. One day, she gets the chance to meet him. However, at the same time, a powerful criminal organization discovers their identities and tries to capture them both. So they have to work together to not only escape but also take down this organization that is causing harm to the city.
In some Spiderman fanfiction, Flash might help by providing an unexpected ally. For example, he could use his popularity or resources to assist Spiderman in a difficult situation. However, Flash often hurts Spiderman in fanfiction too. His bullying nature can lead to Spiderman's self - doubt or put him in dangerous situations, like when Flash's actions draw unwanted attention to Spiderman's secret identity.
In Spiderman fanfiction, Flash might help when he gets involved in a situation where his actions indirectly aid Spiderman. However, he hurts a great deal. His attitude can make Spiderman feel isolated. Since Spiderman already has a lot on his plate, Flash's negative behavior adds to the stress. It can also make it harder for Spiderman to maintain his secret identity as Flash is always looking for ways to expose any weakness in Peter Parker.
In a 'nightwing meets spiderman' fanfiction, they could team up to fight a common villain. Maybe a powerful criminal who has the ability to move between Gotham and New York unnoticed. They would combine their unique skills, Nightwing's acrobatics and combat skills with Spiderman's super strength and web - slinging.