Well, it could be really interesting. Maybe in this fanfiction, Peter Parker picks up Thor's hammer during a big battle. This act would not only shock everyone around him but also change the course of the battle. With the hammer, he could fly faster and strike with more force. And it would also likely have an impact on his relationships with other superheroes. They might see him in a whole new light, as someone who is not just a friendly neighborhood Spider - Man but also a worthy wielder of a powerful Asgardian weapon.
It could be Loki. Since Peter has picked up Thor's hammer, Loki might see him as a new threat. Loki is always after power and causing chaos, and Peter with the hammer would be a powerful force to oppose him.
Well, a few characters have managed to pick up Thor's hammer. Besides Captain America, there's also Beta Ray Bill and Jane Foster, among others. Each had their own circumstances and reasons for being worthy.
In this fanfiction, it's a really exciting concept. Peter Parker, also known as Spider - Man, is able to lift Thor's hammer. This goes against the normal rules in the Marvel universe where only the worthy can lift Mjolnir. It could be that the fanfiction explores Peter's character in a new light, showing his inner worthiness perhaps through his selfless acts as Spider - Man. Maybe it also has implications for his power level, suddenly having the abilities of Thor added to his own.
One possible plot twist could be that when Peter lifts the hammer, it actually has a negative effect on him. Maybe it starts to corrupt him in some way because he's not fully ready to handle that kind of power. Another could be that it's all a trick by a villain who has somehow enchanted the hammer to make Peter think he can lift it, only to use it against him later.
In such a fanfiction, perhaps Peter would gain new powers. Since only the worthy can lift Thor's hammer, it would show that Peter has a pure heart and noble character. He might use the power of the hammer to fight stronger enemies, like those that the Avengers alone couldn't defeat easily.
He might gain new powers or abilities. Since the hammer is a powerful magical weapon, lifting it could unlock some latent potential within Peter. Maybe he can now control lightning like Thor, or he has enhanced strength and durability.
Yes, there are likely to be such fanfictions in the vast world of fan - created content. Fanfiction often explores unique and unexpected crossovers like this one.
In some fanfictions, it could be because Peter has a pure heart. Just like in the MCU, only those worthy can lift Mjolnir. Peter might have proven his selflessness and heroism in a particular situation, which made him worthy enough to lift Thor's hammer.
There could be many people who created such fanfiction. It might be an individual writer who is a big fan of both the Spider - Man and Thor characters and wanted to see what would happen if Peter could lift the hammer. It could also be part of a fanfiction community where different people contribute ideas and sometimes collaborate on stories.