In fanfiction, it might be due to psychological factors. If Spider - Man experiences extreme trauma or self - doubt, it could cause him to lose his powers. He might start to believe that he's not worthy of having them or that he's a danger to those around him. This internal conflict could lead to his powers fading away. It could also be because of a deal he makes with a powerful entity. To save someone he loves, he might give up his powers without fully understanding the consequences.
Perhaps in the fanfiction, a new villain has developed a technology that can suppress superpowers. This villain targets Spider - Man specifically. The device could emit a frequency that interferes with the way his body's cells interact to create his powers. Or, it could be that the spider that originally bit him had some sort of time - limited or conditional effect on his powers, and that time has run out or the conditions have been violated, leading to the loss of his powers.
One reason could be a powerful magic spell cast on him by a villain. For example, a sorcerer who wants to stop Spider - Man from interfering in his evil plans might use a spell that disrupts the source of his powers. Another possibility is that he gets exposed to some sort of radiation or chemical that nullifies the mutation that gives him his powers. Maybe he enters a new dimension where the laws of physics are different and his powers don't work there.
He might first go into denial. He could keep trying to do the things he used to do with his powers, like swing from building to building, only to fall. Then he could start to rely on his intelligence more. Since Peter Parker is a smart guy, he'd use his scientific knowledge to try to find a way to get his powers back. He may also look for allies who can help him, like other superheroes or scientists.
One possible reason could be a difference in ideology. Maybe Spider - Man has a more local - friendly approach to crime - fighting while the Avengers are often involved in large - scale, global threats. He might feel that his skills are better utilized in his own neighborhood, like Queens, rather than in the grand, often cosmos - level battles of the Avengers.
One reason could be false accusations. Maybe someone spread rumors about him being involved in dark magic again, even if he was innocent. In the cut - throat world of Hogwarts politics in fanfiction, such false accusations could cost him his job.
He could develop the ability to combine his chakra with his Spider - Man powers. For example, he could infuse his webs with chakra to make them stronger or even give them different properties like being able to cut through objects. Another new ability could be using his shadow clones in combination with his Spider - Man agility. He could send clones to different locations while swinging around with his webs, creating a more complex battle strategy.
One possible new power could be energy projection. He could shoot out webs of energy instead of just the physical webs. This would not only enhance his offensive capabilities but also give him a new way to interact with his surroundings and immobilize foes from a distance.
Maybe he discovers some dark secrets within his own superhero community or organization. Fearing for his safety and not knowing who to trust, he decides to run away and figure things out alone. For example, if he finds out that some of his allies are involved in unethical experiments related to their powers, he might feel the need to escape and expose the truth from a distance.
In fanfiction, Spider - Man could gain the power of teleportation. This would allow him to quickly move around the city and reach crime scenes faster. He might also develop the power of super strength in his legs, enabling him to jump much higher and farther than before. Additionally, the power to manipulate time, even if just for a few seconds, could be a great addition.
Another possibility is that the Avengers are being manipulated by a villain. The bad guy could be using false information to make the Avengers believe that Spider - Man is a danger. So they go after him without really knowing the truth.
In the fanfiction, it could be that Spider Man has a personal vendetta against one of the Avengers members. For example, if one of them had a past with a villain that Spider Man has a strong connection to, like if an Avenger unknowingly helped the villain in the past, Spider Man might transfer his hatred for that villain to the Avenger and by extension, the whole team.
In the 'Spider Man Becomes Toxin Fanfiction', it could be that Spider Man is tricked into wearing a piece of alien technology that is actually a Toxin - like symbiote in disguise. The symbiote slowly takes over his body and mind, turning him into Toxin. Additionally, the fanfiction might explore the idea that Spider Man's own self - doubt and internal struggles somehow attract the Toxin - like transformation. He may be feeling inadequate or guilty about something, and this negative energy makes him a prime target for the Toxin transformation.