Perhaps it's due to some sort of poison or toxin. In the world of Spider - Man, there are many villains who use chemical weapons. He could have been exposed to a new, unknown substance that affects his nervous system and causes him to faint.
One possible reason could be extreme exhaustion. Peter Parker has a double life as a student and Spider - Man. He might be overworked, not getting enough sleep, and his body just gives out. For example, he could have been fighting multiple villains in a row without a break.
It could be due to some sort of poison or magical spell. In the Percy Jackson universe, there are all kinds of creatures and magic that could cause such a reaction. For example, if he was exposed to a slow - acting venom from a mythical beast, it might gradually make him faint.
Well, one reason could be that he's on a secret mission for S.H.I.E.L.D. that requires him to go undercover and cut off all contact. Maybe he's investigating a new super - villain threat that's too dangerous to let anyone know about.
One possible reason could be a difference in ideology. Maybe Peter Parker feels that Stark's methods are too extreme or not in line with his own moral compass. For example, Stark might be involved in some projects that Peter doesn't agree with, such as using certain unethical technologies in the pursuit of justice.
Maybe it's due to a new and powerful enemy's attack. In fanfiction, authors might create unique villains with abilities that specifically target Peter's weaknesses. For example, if the villain has the power to disrupt Spider - Man's enhanced senses, it could cause Peter to be disoriented and ultimately collapse. Another aspect could be that Peter overuses his powers without proper rest, which exhausts his body and causes him to collapse.
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 reason could be extreme grief. If he lost someone very close to him, like Aunt May in a particularly cruel way, it might shatter his moral compass. Another reason could be mind control. Maybe a powerful villain manages to get into his head and twist his thoughts and values. Also, if he was constantly betrayed by the people he trusted, such as the Avengers or his friends at school, he could gradually turn bitter and evil.
Another reason might be related to some sort of experiment gone wrong. Peter is often involved in scientific research. If there was an accident in his lab, perhaps with a new type of spider - related serum or some other experimental technology, it could have unforeseen consequences on his heart and lead to it stopping.
He might think it's not in line with the real Steve. Fanfiction can be quite far - fetched sometimes.
Well, it might be an exploration of the psychological toll of being a superhero. Peter Parker constantly faces danger, loss, and has to keep his identity a secret. Writers may create 'suicidal peter parker fanfiction' to show how all these factors could potentially break him. Also, in the context of fanfiction, it could be a way to subvert the typical heroic narrative and show a more vulnerable and broken side of the character. However, it's a very heavy and potentially triggering topic.
One reason could be that Peter realizes he still has unresolved feelings for Gwen from his past. Maybe something happens that makes him remember their relationship more vividly.