Maybe MJ. She could be in the area and use her quick thinking. She might find a large awning or something to break his fall, or she could call for help from nearby superheroes like Daredevil who could swing in and save Peter.
It could be Doctor Strange. He could sense Peter's danger and open a portal right below Peter as he jumps out the window. Peter would then fall through the portal and land safely in Strange's Sanctum Sanctorum.
Perhaps in this fanfiction, Peter has some new power or gadget that he's testing. So when he jumps off the building, instead of the usual web - swinging, he activates this new ability which allows him to fly or at least glide to the ground in a very cool and unexpected way.
Well, one possible plot twist could be that instead of falling, he discovers he can fly. Maybe it's a new power he didn't know he had. Another could be that he lands in a parallel universe where everything is different. For example, his enemies are his friends and vice versa.
It could be a character named Jules. But it's been a while since I watched it, so I might not be 100% sure.
It could also be related to his identity as Peter Parker. If he's trying to keep his Spider - Man identity a secret from his friends, he can't fully share his experiences. This secrecy might create a barrier, making him feel like an outsider even among those he cares about. For example, if his friends are sharing personal stories and he has to hold back parts of his own life, he'll gradually feel left out.
Maybe Peter gets poisoned with a toxin that affects his powers. Matt, being a lawyer and having connections, could find an antidote or get help from someone in the medical field he knows. He could also protect Peter while he's weakened, using his martial arts skills to fend off any villains who try to take advantage of Peter's vulnerable state. Matt's ability to move in the shadows would be useful in keeping Peter safe from further harm.
Definitely Tony Stark (if he were still alive in the fanfiction). Tony has always been a mentor to Peter. His vast knowledge and resources could be invaluable in helping Peter deal with whatever problem he has. He could create new gadgets for Peter to use in case his omega situation requires special equipment.
Aunt May is a very likely candidate. She has always been like a mother figure to Peter. She would notice that he's dirty or injured after a day of being Spider - Man and would gently lead him to the bathroom to get cleaned up. It would be a very nurturing moment between them, with Aunt May scolding him a bit for getting into so much trouble but also showing her love through taking care of him.
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.
It's likely to result in serious injury or even death. The height is significant and the impact would be tremendous.
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.