Maybe there's a multiverse event that causes Peter Parker to be transported to the DC universe. He meets Superman first, and Superman is initially a bit wary of this strange new hero with spider - powers. But as they face a common enemy, like Lex Luthor who has somehow gotten his hands on some Oscorp tech, they learn to work together. Peter can use his scientific knowledge from his own world to help Superman figure out how to disable the dangerous tech.
In a Peter Parker and DC crossover fanfiction, Peter could be called to Metropolis by Lois Lane. She's heard rumors of a masked hero in New York and wants to do a story on him. Meanwhile, in Metropolis, there's a new villain causing chaos, someone with powers similar to Electro but on a much larger scale. Peter teams up with the Flash to chase down this villain, with the Flash's super - speed and Peter's web - slinging making for an exciting chase sequence.
First, understand the characters well. For Peter Parker, know his sense of humor, his loyalty to his friends and family, and his struggle to balance his normal life with being Spider - Man. For DC characters like Batman or Superman, study their motives, their moral codes, and their relationships. Then, create a compelling plot. Maybe start with a mystery that draws both universes together, like a strange energy source that's causing disruptions in both New York and Gotham. Keep the interactions between the characters believable. Peter might be in awe of Superman's power at first, but then find ways to contribute with his own unique skills.
One idea could be a crossover where Peter Parker's scientific knowledge helps Mary Marvel when she gets caught in some sort of DC - related technological snafu. Maybe he figures out a way to reverse the effects of a strange device that was meant to weaken her powers.
If we consider Peter Parker and Supergirl. Supergirl is a powerful being from Krypton. Their marriage could involve Peter having to deal with her super - strength and also the fact that she has a different set of values coming from an alien culture. They could work together to protect both Metropolis and New York, combining their powers and intelligence.
Another idea is that Peter discovers the existence of demigods while investigating a series of strange disappearances in Central Park. He stumbles upon Percy who is on a quest. They initially have some misunderstandings as they come from such different worlds, but then they figure out that they can help each other. Percy helps Peter understand the magical side of things, and Peter helps Percy with his knowledge of the city's layout and technology.
One idea could be that Peter Parker gets injured during a fight with a villain and has to use crutches. His friends at school might be really concerned and try to help him out, like Ned bringing his books for him. In the fanfiction, it could show how he still tries to be Spider - Man even with his injury, perhaps using his web - shooters in creative ways to move around while on crutches.
Another possibility is Peter Parker marrying Catwoman. This could be an interesting take as Catwoman is often a morally grey character. Peter could try to bring out the good in her. Maybe in this fanfiction, they meet during a heist where Peter is trying to stop the bad guys and Catwoman is also involved. Their relationship could start as a rivalry and then turn into love.
One idea could be that they meet during a multiverse - related crisis. Peter's quick thinking and Thundra's strength complement each other as they fight side by side. As they spend more time together, they start to develop feelings. Eventually, they decide to get married in a ceremony attended by various superheroes from different universes.
Well, in a fanfiction where Peter Parker turns into a kid, perhaps he could end up at his old school. He'd be faced with bullies again, but this time he has the knowledge and experience of being Spider - Man, even if he's in a kid's body. This could lead to some interesting scenarios where he uses his smarts to outwit the bullies without using his powers directly. Or, he could befriend his younger self's friends in a whole new way, seeing them from a different perspective.
One idea could be that Peter Parker and Captain Marvel are teamed up to face a powerful cosmic threat that's approaching Earth. They initially clash due to their different approaches - Peter is more street - level and cautious, while Captain Marvel is bold and used to dealing with large - scale threats in space. But as they get to know each other better, they start to combine their powers effectively, with Peter using his spider - sense to anticipate the enemy's moves and Captain Marvel delivering powerful blows.
Another fanfiction concept could be that Peter's school starts a new dance club. Peter joins to keep an eye on a suspect he thinks might be involved in some criminal activities. But as he participates in the club, he falls in love with dancing itself. He then has to figure out how to balance his detective work within the club and his growing passion for dance without blowing his cover as Spider - Man.