Maybe Psylocke gets lost in a dimension where Spiderman is the only one who can help her get back. During their journey, they learn about each other's powers and personal struggles, and in the end, their friendship deepens. Spiderman could use his scientific knowledge along with Psylocke's psychic powers to find a way out of the strange dimension.
One idea could be a story where Spiderman has to team up with his greatest enemies to fight a new, more powerful threat from outer space. This would force him to put aside his differences and find common ground with the likes of Doctor Octopus and Green Goblin.
Maybe a plot where Spider - Man has to face a new villain who has the power to manipulate time. This would make for some really interesting battles and strategic thinking on Spider - Man's part. He would have to find a way to defeat the villain without getting caught in the time - warping chaos. Also, a story about Spider - Man traveling to an alternate dimension where his powers work differently could be cool.
One idea could be that the chubby Spiderman has a hard time swinging between buildings due to his extra weight, so he has to come up with new ways to move around the city. Maybe he invents some sort of web - enhanced jetpack. Another plot could involve him being bullied because of his appearance, but then he uses his intelligence and superpowers to prove his worth. For example, he could solve a big scientific mystery that even the smartest minds in the city couldn't crack.
One idea could be Aunt May discovers Peter's identity as Spiderman in a very unexpected way, like she accidentally finds his suit while cleaning. Another could be Aunt May getting kidnapped and Spiderman has to save her without revealing his identity to the bad guys. Or perhaps Aunt May teams up with Spiderman in a community project that turns into a fight against a small - time villain who is causing trouble in their neighborhood.
One idea could be that Spiderman gets transported to the DC universe due to a multiverse glitch. He teams up with Batman to stop a villain who has stolen technology from both universes. Another could be that Peter Parker goes to Metropolis for a science fair and accidentally gets involved in a battle between Superman and Lex Luthor, using his Spidey - sense and skills to help Superman.
Maybe in this fanfic, there's a multiverse crisis that causes parts of New York in the Marvel universe to merge with Gotham in the DC universe. Spiderman and Superman meet and initially have a bit of a misunderstanding due to their different ways of handling things. But then they realize they need to work together to separate the two cities again. Spiderman could use his webs to help Superman contain some of the chaos while Superman uses his strength to move large structures that are in the way.
One idea could be that Spider - Man tries to form his own group of heroes who are neutral in the Civil War. They could be a sort of mediator between Captain America and Iron Man's sides. For example, he recruits some lesser - known heroes like Daredevil or Jessica Jones.
One plot idea could be that Spiderman and Mantis team up to fight a new villain in the city. Mantis uses her empathic abilities to sense the villain's motives, while Spiderman uses his webs and strength to physically combat the foe. Another could be a story where they get accidentally transported to an alternate dimension and have to work together to find their way back home. They might face strange new enemies and allies in this dimension.
Another plot could involve a mad scientist who creates a device that can drain the powers of superheroes. He first targets Superman, but Spiderman gets involved when he sees the chaos in Metropolis. As they try to stop the scientist, they discover that the device has a side effect of giving the heroes new, unexpected powers for a short time. They have to quickly learn to control these new powers while also dealing with the main threat.
For a 'Spiderman into the Spider - Verse fanfic', you could have a plot where the Spot, who has been working on a new super - weapon in secret, manages to open portals to multiple universes all at once and unleashes a horde of minor villains from each. The Spider - People from different universes have to band together not only to fight these villains but also to close the portals. There could be a sub - plot about a relationship developing between two Spider - People from very different universes, like one from a steampunk world and another from a world of magic. This relationship could add an interesting emotional layer to the story as they struggle to save the multiverse.