It could also be due to external factors affecting Izuku's mental state. For instance, if there are threats to his friends or the school, and Aizawa's actions or decisions seem to be hindering Izuku's ability to protect them. Izuku, being the determined and passionate character he is, might snap at Aizawa in order to take matters into his own hands. Moreover, in some stories, the author might be exploring a different side of Izuku's personality, showing that even the meekest characters can have a breaking point when provoked in the right (or wrong) way.
One reason could be that Izuku has been pushed to his limit. Maybe Aizawa has been overly critical or strict in a way that Izuku can't take anymore. For example, if Aizawa constantly doubts Izuku's abilities despite his efforts, it could lead to Izuku snapping.
I'm not sure of specific 'izuku snaps at aizawa fanfiction' titles off the top of my head. You could try searching on fanfiction platforms like Archive of Our Own. They usually have a wide variety of fanfics, and you can use those keywords in the search bar to find relevant stories.
In some fanfictions, Aizawa might be under the influence of a villain's quirk that makes him act against his will. So, he kidnaps Izuku, but later on, he realizes what he's done and tries to make amends. This could lead to a story full of drama and redemption.
Well, it could be that Monoma is constantly taunting Izuku about his quirk or his status at school. Izuku, usually patient, finally snaps under the pressure of Monoma's relentless jabs. Maybe Monoma makes a comment about how Izuku got into U.A. through some sort of fluke, and Izuku just can't take it anymore and lashes out verbally or even physically.
It could be Aizawa himself if he's being controlled by something or has some sort of ulterior motive that is not in Izuku's best interest. But if not Aizawa, then there could be a hidden villain who is manipulating Aizawa to kidnap Izuku.
One possible reason could be that Naruto has been pushed to his limit. Maybe Sasuke has said or done something that really strikes a nerve. For example, if Sasuke were to mock Naruto's dreams or the friends he has lost in his journey to protect the village. Naruto is a very emotional character, and when it comes to Sasuke, his emotions run even deeper. So, if Sasuke were to continuously reject Naruto's attempts at friendship or redemption in the fanfiction, it could cause Naruto to snap.
One scenario could be that Izuku is on the roof to get some fresh air and clear his head. Aizawa, being the observant teacher he is, follows him there. He could then share some of his own experiences with Izuku, like how he overcame difficulties in his youth, which would inspire Izuku and strengthen their relationship in the fanfiction world.
Well, it could be about Izuku confronting Aizawa over some misrepresentation in the fanfiction. Maybe Izuku doesn't like how Aizawa is being portrayed as too strict or unfair in the fic.
Sometimes, the source material itself can be a factor. If there are major changes in the official My Hero Academia storyline related to Izuku, it might make the author's original concept for the fanfiction no longer viable. Or perhaps they had planned the fanfiction to be part of a certain arc in the series, and when that arc didn't play out as they expected in the official story, they abandoned their work.
Well, 'izuku snaps' fanfiction could be about the character Izuku reaching a breaking point. It might explore a situation where he's pushed too far by the challenges he faces, like dealing with villains or the pressure from school. Maybe he snaps and does something completely out of character, or perhaps it's a moment of self - discovery where he realizes he has to change his approach to things.
In fanfiction, Izuku snapping at Shinsou could be due to various reasons. Maybe there's a misunderstanding between them, like a competition for a certain opportunity at school. Izuku, being under a lot of pressure, might lose his temper.