There could be a mind - control situation. A villain has taken over Peter's mind and forces him to jump off the building. However, Peter's subconscious is fighting back, and as he falls, he starts to break free from the control, ready to face the villain once he lands safely.
He could be trying to save someone. Maybe a civilian is falling from a higher floor, and Peter jumps off to catch them and use his webs to swing them to safety.
It might be part of a training exercise. Peter is always looking to improve his skills, and jumping off a building and relying on his reflexes and powers to survive could be a new and extreme form of training in the fanfiction world. He wants to push his limits and see what he can really do.
Peter's own quick thinking helps him survive. He could use his surroundings during the fall. For example, if there are ledges on the building, he can use them to break his fall. He can also calculate the best way to land, using his acrobatic skills that come with his powers, so that he minimizes the damage to himself.
Maybe she was in a deep state of depression or facing extreme stress that she saw no other way out.
It could be due to extreme emotional distress, like severe depression or a traumatic event.
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.
In some fanfiction, Peter Parker might leave the Avengers because he feels out of place. Maybe he realizes that his style of heroism doesn't quite fit with the more organized and sometimes bureaucratic way the Avengers operate. He could also leave due to personal reasons, like wanting to focus more on protecting his local neighborhood in Queens rather than getting involved in global Avengers - level threats.
Peter Parker is a very relatable and endearing character. His journey as a superhero while also dealing with normal life problems makes for great fanfiction. People love to explore different scenarios for him, like his relationships or new adventures.
Another reason could be related to Peter's mistakes. He may make errors during a mission that put the whole team or the city at risk. Tony, who has a lot of responsibility on his shoulders, might yell at Peter as a way to make him understand the seriousness of his actions and to prevent future mistakes.
In a fanfiction where Peter Parker falls off a mountain, it could lead to various scenarios. Maybe he uses his spider - abilities to try and save himself mid - fall, like shooting webs to catch onto ledges. It could also be a moment of self - discovery, as he faces the possibility of death and realizes things he hadn't before.
Maybe he feels overwhelmed. The Stark internship might be too intense, with high expectations and a lot of pressure. Peter could be a regular kid at heart who just wants a normal life, and the internship takes away too much of his time and energy.
Wanda Maximoff might be a key character too. Her powers were a big concern in the Sokovia Accords situation. Peter could tell her off for not being more careful with her powers and for getting involved in the conflict on Team Cap's side. Also, Clint Barton, Hawkeye, who came out of retirement to support Team Cap. Peter might criticize him for coming back into the fray and adding to the chaos instead of staying out of it.