One idea could be that Peter Parker gets a prosthetic after a particularly dangerous battle with a villain. Maybe his leg is severely injured and he has to adapt to the new prosthetic while still maintaining his superhero duties. He could struggle at first with the balance and movement, but with his determination, he eventually masters it and even modifies the prosthetic to have some special features like enhanced jumping ability.
His relationship with Aunt May could become more complex. She might be overly worried about him and his ability to cope with the prosthetic. There could be a lot of tender moments where she tries to take care of him more than before, which Peter might initially resist as he wants to be independent.
Peter could get a dog. A loyal dog would be a great companion for him, following him around during his daily life and even being a sort of sidekick. It could sense danger and bark to alert Peter when something was wrong.
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.
It could be a vengeful criminal that Spider - Man has put away in the past. This criminal has spent years in prison plotting his revenge and finally gets the chance when Peter is vulnerable. Maybe he manages to ambush Peter in an alleyway while he's on his way home from school or work.
One idea could be that Peter uses his spider - abilities to help on the farm. For example, he can use his super strength to lift heavy farming equipment or his agility to quickly harvest crops. Maybe he becomes a farmer to get away from the chaos of the city and superhero life for a while, finding peace in the simple life of farming.
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.
One idea could be that Peter Parker gets accidentally transported to the Justice League's universe. He could initially be seen as an outsider, but then prove his worth with his spider - sense and acrobatic skills during a battle against a common enemy. For example, against a powerful alien invader where his ability to quickly assess threats and react would be very useful.
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 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.
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.