One idea could be that the OC is reincarnated as a relative of Peter Parker. This would create an interesting dynamic as they would have an in - built connection to the main Spider - Man character. They could inherit some of Spider - Man's powers in a different way, perhaps through a scientific experiment gone wrong that was related to Peter's own origin.
Another plot could involve the OC being reincarnated in a different universe within the Spider - Man multiverse. In this new universe, the rules of being a superhero are different. Maybe the OC has to learn how to use their powers without the guidance of the traditional Spider - Man mentors. They might also face different villains who have unique powers that the OC has never encountered before.
A third plot idea is that the OC was a villain in their past life and is reincarnated with a chance to be a hero. They struggle with their past identity and the urge to use their powers for evil, but also have a new - found sense of justice. This internal conflict could be a major part of the story, as they try to prove themselves to the other heroes and to themselves that they can be a force for good.
One idea could be an OC who is a new student at Peter's school and has a hidden power related to technology. They end up helping Spider - Man with a villain who is hacking into all the city's tech systems.
One plot idea could be that the Spider Man OC and Felica team up to take on a new villain in the city. This villain could have a power that is specifically designed to counter both of their abilities, forcing them to work closely together and develop new skills. Another idea is that Felica discovers the identity of the Spider Man OC by accident, and this knowledge creates a whole new dynamic between them, with trust and secrecy being major themes.
One idea could be that the OC has a special power that can either enhance or counteract Venom's abilities. For example, the OC might be able to emit a frequency that calms Venom when he's in a rage. Another plot could involve the OC being from a different dimension and getting stuck in Spider - Man's world, and Venom takes an immediate interest in this strange new being. They could start as enemies but gradually form an alliance as they face common threats.
An interesting OC for an Ultimate Spider - Man fanfiction could be a mutant who has spider - like abilities but also some other powers that set them apart. For instance, they might have the ability to communicate with spiders on a telepathic level. This OC could start out as an outcast in society, just like Peter Parker, but their powers are a bit more extreme and they have to learn how to control them. They could initially be seen as a threat by Spider - Man but then they team up to fight a greater evil.
One idea could be a crossover between Spider - Man and an original character (OC) who has the power to manipulate time. The OC could accidentally disrupt the timeline in Spider - Man's world, leading to all sorts of chaos like villains getting released early or important events not happening as they should. This would force Spider - Man to team up with the OC to fix the timeline.
Another plot idea is that the OC is a scientist who accidentally creates a new type of symbiote. This symbiote has different properties compared to Venom and Carnage. Spider - Man has to team up with the OC to control and understand this new creation, leading to a lot of action and character development.
Another plot could involve the OC reincarnating into an existing character's body. This would lead to a lot of internal conflict as they try to adjust to the new identity while still having memories of their past self. They could also use their new position to change the course of events in the RWBY universe.
One idea could be that the OC is reincarnated as a member of a powerful but long - lost clan in the Naruto world. They then have to discover their clan's secrets and powers while also dealing with the ongoing conflicts in the shinobi world. For example, they might find a unique jutsu that was lost with their clan.
One idea could be exploring the different Spider - People's home universes in more detail. For example, showing what Miles Morales' daily life in his universe was like before becoming Spider - Man. Another could be a team - up between Miles and an older, more experienced Spider - Person from a different universe to face a new and powerful villain.
Perhaps there's a fanfiction where Spider Man and Spider Gwen accidentally swap powers. They have to learn how to use each other's abilities to fight crime. This would lead to some really funny and also challenging situations as they get used to different ways of web - slinging and sensing danger.