Perhaps Harry witnesses Snape being extremely unfair to a group of students, like constantly giving them detention for no good reason. Harry decides to take a stand and gathers statements from the students. He then goes to the Hogwarts board of governors and presents his case, leading to Snape's dismissal.
In some fanfictions, it might be due to political reasons within Hogwarts. For example, if there is a power struggle between different factions, Snape could be seen as a threat or a liability to one side and they find a way to get him fired. His loyalty has always been somewhat in question in the eyes of some, so it could be exploited.
One possible reason could be Snape's unfair treatment of Harry and his friends. Snape often showed blatant favoritism towards Slytherin students and was overly harsh on Gryffindors, especially Harry. This constant bias could lead Harry to want him fired. Another reason might be Snape's connection to the Dark Arts. Harry, having faced Voldemort, might be worried about Snape's knowledge and use of dark magic within Hogwarts. Also, Snape's generally unpleasant demeanor towards students could be a factor. His sarcastic remarks and cold attitude might make Harry think that he is not a suitable teacher for Hogwarts students.
Well, it could start with a dream or a prophecy. Harry has a strange dream about Snape that he can't shake off. He starts to observe Snape more closely in real life and realizes that there's more to him than he thought. Meanwhile, Snape notices Harry's change in behavior towards him. As they interact more, they find common ground in their love for magic and their shared experiences of loss. This mutual understanding could lead to a situation where Harry, driven by his new - found respect and affection, kisses Snape. It's a very different take on the relationship between the two characters compared to the original story.
Well, perhaps it was because of a conflict with a powerful figure. Maybe she had a huge argument with the Headmaster or someone from the Board of Governors. If she strongly opposed a decision that the higher - ups were very much in favor of, it could lead to her dismissal. For instance, if there was a plan to cut down on certain magical subjects that she thought were essential for students' education. And in a fanfic world, there could be some made - up reasons too, like a mysterious prophecy that said her presence at Hogwarts would bring some great danger, so they fired her to avoid it.
One possible plotline could be that Remus and Snape are forced to work together on a special mission within Hogwarts. They initially clash due to their past differences, but as they face various challenges together, they start to respect each other more. Then, they both have a connection with a third character, perhaps a new teacher at Hogwarts. They form an unlikely alliance to protect this person from some dark forces that are emerging in the wizarding world. This new bond gradually develops into a deep friendship that has elements of a threesome relationship in terms of their shared experiences and mutual protection.
One possible plotline could be that Harry discovers a plot against Snape before it's too late. Maybe he overhears some Death Eaters planning to ambush Snape while he's on a solitary mission. Harry then uses his invisibility cloak and magic skills he's learned over the years to outwit the Death Eaters and save Snape. This would show Harry's growth as a wizard and his ability to set aside past differences with Snape.
Well, there could be a plotline where Snape's father was an inventor in the wizarding world. He might have created some powerful magic items or spells that were lost or forgotten. Snape, in the fanfiction, could be on a quest to find and revive his father's work. Another idea is that Snape's father was a key figure in a war long before Voldemort's rise, and his actions had consequences that Snape has to deal with in the present day of the fanfiction. There could also be a plotline where Snape's father was a mentor to some other important character, and this connection has implications for Snape's life and the overall story.
Maybe Harry goes back to the time when Snape was being bullied by James Potter and his friends. Harry, knowing the importance of Snape in the future, steps in to stop the bullying. This act of kindness from Harry could lead to Snape having a different view of the Gryffindors and also a different attitude towards Harry himself. It could also make Snape more confident and less resentful, which might in turn affect how he behaves during the wizarding war.
One possible plotline could be Snape finding drunk Harry in the Hogwarts corridors. Snape, being the strict teacher, might initially be angry but then realizes Harry is in a vulnerable state. He could take Harry to his office to sober him up and in the process, they have a conversation that reveals some hidden feelings or understanding between them.
One possible plotline could be that Harry discovers Snape's true motives much earlier. Maybe he stumbles upon Snape's memories that show his complex relationship with Harry's mother. This new understanding makes Harry see Snape in a different light. They start to have secret meetings where Snape teaches Harry advanced magic, away from the prying eyes of others at Hogwarts. Their relationship gradually evolves from one of enmity to an unspoken bond.