In the fanfiction, it might be that Fudge makes a huge blunder. For example, he wrongly accuses a large group of innocent wizards of being dark wizards. Harry, with his sense of justice, stands up against this false accusation. He uncovers the truth and the public outcry forces the Ministry to fire Fudge.
Well, it could be that Harry discovers some major misdeeds by Fudge. Maybe Fudge has been covering up dark magic activities within the Ministry. Harry then finds evidence and presents it to the proper authorities, leading to Fudge's dismissal.
The Weasley family, especially Arthur Weasley, could be involved. Arthur, being an employee at the Ministry, might know some inside information about Fudge. He could assist Harry either directly or by providing some useful connections within the Ministry to get Fudge fired.
In such a fanfic, perhaps Harry discovers some long - hidden, damning secret about Dumbledore. Maybe it's related to Dumbledore's past actions with Grindelwald. Harry, being the honest and justice - seeking person he is, feels compelled to expose this secret, which then leads to Dumbledore being fired from his position at Hogwarts.
One possible plot could be that due to some false accusations of improper teaching methods, Aizawa gets fired. His students then band together to prove his innocence. They collect evidence of his effective teaching, like how he has helped them improve their quirks and grow as heroes in training. Eventually, they manage to clear his name and he is reinstated.
Well, it could be that Lloyd made a major mistake in his strategic planning for the Geass-related operations. Maybe he miscalculated something crucial about the enemy's movements or capabilities, which led to a significant setback for his side. And as a result, his superiors decided to fire him.
Hermione could be a great help. She is very intelligent and resourceful. She could help Harry find evidence against Snape. For instance, if Snape is suspected of cheating in grading, Hermione could use her knowledge of Hogwarts' grading system and records to dig up proof.
Well, in a fanfiction, SpongeBob could be fired due to a misunderstanding. For example, Mr. Krabs misinterprets something SpongeBob says as a threat to quit. SpongeBob is devastated. He then tries different jobs like being a delivery boy for a seaweed company. However, he misses the Krusty Krab so much. In the end, Mr. Krabs figures out the truth and welcomes SpongeBob back with open arms.
Maybe Fudge was starting to turn against the wizarding community in more extreme ways. For example, if he was planning to persecute Muggle - borns more harshly or side with the Death Eaters secretly. Harry, being a defender of justice and equality in the wizarding world, would not tolerate such actions and might have been pushed to kill Fudge to stop his evil plans.
In this kind of fanfiction, perhaps Harry discovers some serious misdeeds by Snape that lead to his dismissal. For example, Snape might be caught unfairly favoring Slytherin students in a major way, like giving them unearned high marks in exams while unduly punishing Gryffindors. Harry, being the observant and just character he is, would report this to the proper authorities at Hogwarts, which could be Dumbledore or the school board. And this could start the process of Snape getting fired.
One possible reason could be his performance at work. Maybe he repeatedly failed to meet his targets or made too many mistakes. For example, if he was in a sales job and couldn't close enough deals, his boss might decide to let him go.
It could be a new administrator at the school who has a very different vision of how hero training should be conducted. This person might see Aizawa's methods as too old - fashioned or too lax, even though they are actually effective. So, they push for his dismissal.