The fanfiction may present Snape as having a different set of values and priorities. If these values align with protecting Hermione, she will feel safe. Maybe Snape in these stories is more focused on the well - being of the younger students, especially Hermione, rather than his usual preoccupations in the original story.
One reason could be the re - imagining of Snape's character. In fanfiction, he might be kinder and more understanding towards Hermione than in the original story. So, she feels safe in his presence.
One possible reason could be that Snape has shown unexpected kindness to Hermione in the fanfiction. Maybe he has protected her from some danger secretly, which makes her feel she can rely on him and thus feel safe.
One reason could be Snape's knowledge. Hermione, being a knowledge - seeker herself, might feel safe knowing that Snape has a vast understanding of magic, especially the darker aspects. So, she believes he can keep her safe from any threats related to that knowledge.
Well, it could be that the fanfiction author has created a unique backstory. For example, Snape could have saved Hermione's life at some point in the past, and she now has this deep - seated sense of security around him. Also, he might be a source of knowledge for her, and his presence, while initially intimidating, becomes reassuring as she realizes he won't let harm come to her in matters related to magic and the school.
Often, it starts with a shared experience. For example, they might face a dangerous magical creature together. After that, Snape might show concern for Hermione's well - being, which begins to build her sense of safety around him.
Perhaps it's because Snape is a complex character in the original story. Fanfictions might explore his character in ways that make Hermione seem protected in those fictional scenarios. For example, some fanfictions could depict Snape using his knowledge and power to shield Hermione from various threats within the magical world they inhabit.
Hermione is also very confident in her knowledge. Snape is an expert in Potions, but Hermione is no slouch either. So, when Snape tries to undermine her in Potions class, she might respond with sarcasm. For example, if Snape corrects her in a way that she thinks is wrong, she could say 'Of course, Professor, your infinite wisdom must be right' in a sarcastic tone.
In fanfiction, sometimes authors like to break boundaries and explore 'what - if' scenarios. For the 'Snape cheats on Hermione' idea, it could be a way to create drama and conflict. They might be interested in exploring the emotional turmoil it would cause for Hermione, or how it could change the relationships within the wizarding world they've created in their story. It could also be a way to subvert the typical hero - heroine relationships we see in the original series.
One possible reason could be a misunderstanding. Maybe Hermione thought Snape was involved in some dark plot against her friends. In the wizarding world, there are often secrets and deceptions, and if she got some false information, it could lead her to take such drastic action.
Some fanfiction writers might do it for shock value. They want to create a very different and extreme situation compared to the original story to attract readers' attention.
One possible reason is Snape's prejudice. He might have some sort of bias against Gryffindors in general, and Hermione, being a very Gryffindor - like student, gets the brunt of it. He may expect her to make mistakes typical of Gryffindors like being overly bold without thinking. Another factor could be that Hermione is so intelligent and inquisitive that Snape feels threatened. He likes to be in control of the knowledge in his classroom, and Hermione's constant questions and thirst for knowledge might make him act tough towards her.