Miles Morales could be a great addition. He has his own unique set of powers and a different perspective compared to Peter Parker. His inclusion could bring new energy and storylines to the team.
Gwen Stacy as Spider - Woman. She is a fan - favorite character and her addition to the team would add a female perspective and some interesting romantic and friendship dynamics with the other members.
One character that could be added is a new love interest for Peter Parker. Maybe a scientist who works at Oscorp and has her own set of skills and secrets. Another could be a young mutant who looks up to Spider Man and wants to be his sidekick. This would add a new dynamic to the story as Spider Man has to train and protect the young mutant.
One possibility could be Boruto as a new - age Naruto - like character. Sarada, with her Sharingan and Uchiha heritage, could be another member, similar to Sasuke. And for the third member, maybe a new character like a young ninja from a small and previously unrecognized clan who has a unique chakra ability. This new character could bring in fresh dynamics to the team.
Maybe a villain who can transform into different animals. He could use this power to stalk Spider - Man in the city, changing forms to blend in and then attack when least expected. This would keep Spider - Man on his toes as he tries to figure out the pattern of the villain's attacks and how to counter this shape - shifting ability.
A plot could involve the Spider - Man team getting stranded in an alternate dimension. They would have to find a way to get back home while also dealing with the unique challenges and threats of that dimension. This could include new villains, different versions of themselves, and strange new powers.
How about a new villain created specifically for the fanfiction? A being made up of the combined negative energy from all the spider - verses. This entity could be called the 'Void - Spider' and it feeds on the chaos and destruction that often follows Spider - Man in his battles. It would be a very powerful and unique threat that the Spider - Men from different universes would have to face together.
Gwen Stacy is an obvious choice. In different universes, she has different relationships with Spider - Man. Another could be Mary Jane. She has always been an important part of Spider - Man's life. Black Cat might also be in the harem as she has a complex and flirtatious relationship with Spider - Man in the comics.
One interesting character could be Peter Parker's aunt. She often provides a grounding force in his life and her reactions to the new girl could add depth to the story. Another might be one of Spider - Man's villains, like Green Goblin. His presence can create conflict and tension in the fanfiction, especially if he targets the new girl to get to Spider - Man.
Maybe a brilliant biologist who has developed a way to enhance human physical abilities through genetic manipulation. A former S.H.I.E.L.D. agent who has inside knowledge of all kinds of secret operations and is an expert in combat and espionage. Also, a young inventor from a small town who has created some amazing but unrefined gadgets that catch Stark's attention.
The Green Goblin would be a great main antagonist. His chaotic and unpredictable nature could pose a real threat to Spider - Man. He could have a new and improved glider and pumpkin bombs, and his goal could be to take over the city by causing mayhem and destruction.
Loki could be a great main villain. He could trick Spider - Man into believing that Thor is a threat to Earth and set them against each other. Then, while they are fighting, Loki could carry out his real plan which might involve stealing a powerful artifact from both Asgard and Earth.