A plotline could be that Snape is framed for a crime he didn't commit, and Harry, who trusts him, is the only one who believes in his innocence. Harry then sets out to prove Snape's innocence, facing many obstacles and enemies in the process. This would be a great twist on the typical relationship between them in the original series.
Perhaps in this fanfiction, Snape shows a side of himself that is completely different from what Harry has known. He might be more open and honest with Harry, sharing secrets that make Harry believe he can be trusted. Like Snape might disclose some long - held information about Harry's parents that only he knew, which makes Harry think Snape has been on his side all along.
Perhaps in this fanfiction, Snape has proven himself to Harry in some extraordinary way. Maybe he has saved Harry's life multiple times or has shown his true loyalties that were hidden in the original story. It could also be that Snape has some special connection with Harry that makes Harry trust him unconditionally.
One possible reason could be that Snape shows a different side to Harry in the fanfiction. Maybe he protects Harry secretly from some hidden threats that others are unaware of, which makes Harry start to trust him.
As the story progresses, they might start to work together more closely. Snape could be teaching Harry some advanced magic that no one else knows, and through this process, they build a bond. Harry begins to understand Snape's past better and realizes that they have more in common than he thought, like their love for Lily Potter in different ways.
Perhaps in the fanfiction, there is a prophecy that Snape will cause great harm to Hogwarts. Harry, being the hero, feels it's his duty to stop Snape. He starts to gather evidence of Snape's wrongdoings, which are not obvious at first. As he digs deeper, he uncovers a web of lies and deceit that Snape has spun. This leads to a confrontation where Harry uses his magic skills and the loyalty of his friends to destroy Snape's influence over the school and the other wizards. Snape might have been planning to use dark magic to take over Hogwarts, and Harry is the only one who can prevent it.
In this fanfiction, their relationship could develop in a rather unexpected way. Maybe Snape initially approaches Harry for his own reasons, but as time goes on, a real bond forms. Harry, who has always been in need of someone to trust, finds in Snape a kind of stability. Snape, on the other hand, might change his attitude towards Harry completely. He might stop being so cold and distant and instead become a warm and reliable figure for Harry. This transformation in their relationship is likely to be a central part of the fanfiction's plot.
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.
One possible plotline could be that Harry breaks a major Hogwarts rule, like sneaking into the Forbidden Forest. Snape catches him and decides that a severe punishment is in order, which in this case is spanking. Another could be that Harry fails a very important Potions test repeatedly, and Snape, frustrated with his lack of progress, resorts to this extreme form of discipline. However, these are all just fan - created ideas and not part of the official story.
In some fanfictions, the plot could revolve around Snape teaching Harry about the Dark Arts in a way that Dumbledore never would. Harry might become more proficient in defensive spells against the Dark Arts but also be more exposed to the darker side of magic. This could create a moral dilemma for Harry as he grows up. Additionally, the relationship between Harry and Draco Malfoy could be completely different, as Snape's influence on Harry might make him less likely to be enemies with Draco from the start.
One possible plotline could be that while Snape is mentoring Harry, some dark magic incident occurs that results in Harry's unexpected mpreg situation. Snape then has to not only continue mentoring Harry in magic but also deal with this strange and difficult situation, perhaps protecting Harry from those who would judge or harm him because of it.