It could be the Green Goblin. He's always been one of Peter's toughest foes and poisoning him would be a devious way to take him down.
Maybe Doctor Octopus. He's a brilliant scientist and could have created a special poison just for Spider - Man. He might have done it to prove his superiority in both intelligence and power.
It could be a vengeful criminal that Spider - Man has put away in the past. This criminal has spent years in prison plotting his revenge and finally gets the chance when Peter is vulnerable. Maybe he manages to ambush Peter in an alleyway while he's on his way home from school or work.
A new character could be introduced as his dance partner. Maybe a transfer student from another country who has a unique dance style. This character could bring a fresh perspective to Peter's life, teaching him new moves and also learning about his world as Spider - Man. They could form a fast friendship based on their shared love for dance.
One option is Pepper Potts. She is intelligent and has a strong will. In a fanfiction, she might see the potential in Peter and they could develop a relationship. Pepper could also help Peter deal with the business side of being a superhero, like Tony Stark did, and they could fall in love over time.
The AI itself could be a main character. It could have a name like Nova or something cool. And then there could be Peter's aunt May, who might be involved in the story when she discovers Peter's AI project and has some concerns about it at first but then comes to see its potential.
Maybe Doctor Octopus. He has always been obsessed with power and knowledge. He might kidnap Peter to figure out the secret behind his spider - powers. He could think that by studying Peter, he can enhance his own mechanical arms or gain some new form of power that would make him the most feared villain in the city.
The Green Goblin could be a great main villain. He might target Peter Parker's daughter to get revenge on Spider - Man. Just like he did with Gwen Stacy in the original story, he could pose a serious threat to her.
It could be a new super - villain introduced in the fanfiction. Maybe a villain with powers that are specifically designed to counter Spider - Man's. For instance, a villain who can manipulate technology and uses it to disable Peter's suit and then delivers a fatal blow.
Ned could be another main character. He could come over to Peter's place to keep him company while he's in pain. They could end up playing video games or Ned could be trying to cheer Peter up by showing him some new Star Wars collectibles he got.
One possible reason could be a misunderstanding. Maybe Peter has been acting secretively about his Spider - Man activities, and his team misinterprets it as him being up to something bad. For example, if he has to disappear suddenly to fight crime, his team might think he's ditching them for other, less noble reasons.
One possible meaning could be a sign of his individuality. In the world of fanfiction, Peter might use tattoos to set himself apart from the normal, expected image of Spider - Man. It could also represent a new phase in his life, perhaps a more rebellious or self - discovery phase.