A story could start with Spider - Man and Thor in a battle against a common enemy. In the heat of the battle, Thor is knocked out and his hammer is lying there. Spider - Man, without thinking much, tries to pick it up to use it against the enemy and to his surprise, he can lift it. This sudden turn of events then sets the stage for the rest of the story.
It could start with Spider - Man being in a slump. He's doubting himself and his abilities. One day, he stumbles upon Thor's hammer in an abandoned place. At first, he doesn't believe he can lift it. But then, remembering all the times he's saved the day, he decides to give it a shot. As he lifts it, a surge of energy runs through him. This gives him new confidence and the story could then focus on how he uses this new - found ability and the hammer to face his inner demons and external threats.
One possibility is that Batman lifting Thor's hammer could create a rift between him and the Justice League. Some members might be jealous or worried about his new - found power. Superman, for example, might be concerned that Batman is getting too powerful. On the other hand, Thor himself could come to Earth to retrieve his hammer and there could be an epic battle or an unexpected alliance between the two.
Well, if Spider - Man lifts Thor's hammer, it would mean he has the worthiness to do so. In the Marvel universe, only those who are pure of heart can lift Mjolnir. So it could imply that Spider - Man is not only a hero in terms of his actions but also in his very essence. It might also give him new powers or abilities related to Thor's powers, like control over lightning perhaps.
It might make them more equal. Thor would see Spider - Man in a new light, as someone worthy like himself.
Thor would probably be shocked at first. His hammer is something very personal and a symbol of his power and worthiness. But then he might see the potential in Spider - Man and be proud that someone else worthy has been able to wield it.
The clash of different universes. Batman is from DC and Thor is from Marvel. Combining them in a fanfiction where Batman lifts Thor's hammer is exciting because it brings together two very different mythologies. Batman is a human with no superpowers (except his great intellect and physical skills) and Thor's hammer is a magical, god - like weapon.
In this fanfiction, the writer might be exploring a different aspect of the characters. Spider - Man is known for his intelligence and his ability to adapt. It could be that he figures out a way to manipulate the hammer's magic. He might use his scientific knowledge to find a loophole in the enchantment. For example, he could analyze the energy signature of the hammer and find a frequency or pattern that allows him to interact with it in a way that enables him to pick it up. This would be a really interesting take on the characters and their powers.
One possible plot could be that in a universe where the rules are a bit more fluid, Spider - Man finds himself in a situation where he has to lift Mjolnir to save the day. Maybe the Avengers are all incapacitated and only he can reach the hammer. He approaches it with his usual self - doubting self, but his pure heart and strong sense of responsibility allow him to lift it. With Mjolnir's power, he then battles against a powerful villain like Thanos, using both his spider - abilities and the power of Thor's hammer.
Well, in the fanfic, Spider - Man lifting Thor's hammer might be a sign of a new level of power or respect within the superhero community. It could also lead to new storylines where he has to take on greater responsibilities, like Thor does with his hammer. He might gain some of Thor's powers or a connection to Asgardian magic too. It's a really interesting concept that can open up a whole new world of possibilities for the character and the story.
It could be due to a cross - over event. Suppose there was a rift in the fabric of different fictional universes. Harry Potter, being in the wrong place at the right time, stumbles upon Thor's hammer. And because he has a pure heart (which is often a requirement to lift Mjolnir), he is able to pick it up and wield it, much to the shock of both the wizarding community and the Asgardians.
Fanfiction often takes creative liberties. It could be that there is a cross - over event that changes the nature of Thor's hammer's worthiness test. Maybe a powerful magical entity in the Harry Potter universe meddles with the hammer's magic. Harry Potter has shown great moral fiber throughout his adventures. His ability to love deeply, his sense of justice, and his unwavering determination against evil could be seen as the 'worthiness' factor by the hammer's magic, allowing him to lift it.