One possible reason could be Snape's unfair treatment of Gryffindor students. Hermione, being a strong advocate for justice, might not tolerate his constant jabs at her house. For example, in the original story, Snape often took points from Gryffindor without what Hermione might consider proper cause. In fanfiction, this could be exaggerated, leading to her blowing up at him.
One key moment could be in the potions class. Snape might be unfairly criticizing Hermione's potion - making skills, and she just refuses to take it silently and stands up to him, stating her case clearly. Another moment might be when Snape is being overly harsh on one of her friends, and Hermione steps in, protecting her friend and facing Snape's wrath head - on.
She might use her magic in a very direct way. For instance, she could make all of Snape's potion ingredients spill over or cause his wand to fly out of his hand.
It often changes the perception of Snape among other characters. When Hermione stands up for him, some characters who previously disliked or distrusted Snape start to question their own views. For example, in a fanfic, after Hermione's defense, Ron might start to see Snape in a new light and be less hostile towards him.
In this fanfiction, Hermione standing up to Snape might cause a rift in the Hogwarts faculty. Some teachers may side with Hermione, seeing Snape's meanness, while others might defend Snape. This could create chaos in the school and lead to a whole new set of adventures for Hermione and her friends as they navigate this new, more complex situation.
He might initially show annoyance. After all, Hermione is often seen as a know - it - all in his eyes. But his sense of justice and his underlying good nature (despite his cold exterior) would kick in. He'd untie her in a rather brusque manner, but then start to question her about how she got into this mess. Depending on her answer, he might offer some cryptic advice on how to avoid similar situations in the future.
A great fanfic could be where Hermione stands up for Snape when some other characters are gossiping about his past as a Death Eater. She might argue that people should be judged by their present actions and not be condemned forever for past mistakes. She could point out how Snape has risked his life countless times to protect the students at Hogwarts, like when he tried to keep the Death Eaters at bay during the school's attacks. This shows that Hermione recognizes his true worth and is not afraid to go against the popular opinion to defend him.
Well, it could be about Severus Snape coming to Hermione's aid in some difficult situation. Maybe she's facing problems at Hogwarts like bullying from other students or difficulties in her studies, and Snape, despite his usually stern nature, decides to help her get through it. It might explore a different side of their relationship, one that we don't see much in the original books.
The 'time - travel' trope is also quite common. For example, Hermione might go back in time and interact with a younger Snape, which can lead to all sorts of new storylines and character developments.
One great Snape and Hermione fanfiction is 'The Unbreakable Bond'. In this story, Hermione discovers a hidden side of Snape during her research in the Hogwarts library. Their relationship starts as a mentorship but gradually evolves into a deep friendship that defies the expectations of the wizarding world. It beautifully portrays their individual characters and how they can complement each other.