In fanfiction, the author might want to explore Snape's past more deeply. Maybe there are events in his life that could have made him truly side with Voldemort. For example, if he had been more influenced by the dark arts from a younger age or had different relationships with other dark wizards that pushed him towards Voldemort. Also, it could be a way to show how different choices could have changed the whole 'Harry Potter' story.
In some fanfictions, Snape may be depicted as truly on Voldemort's side. Fanfiction allows for creative reinterpretations of the original story. However, this goes against his complex and ultimately heroic role in the official 'Harry Potter' series. In the canon, Snape was a double agent, secretly working against Voldemort to protect Harry and help bring down the Dark Lord.
One possible reason could be that Snape fails to deliver crucial information. Voldemort is a very demanding and unforgiving master. If Snape doesn't give him accurate details about the Order of the Phoenix's plans, for example, Voldemort would surely be enraged and punish him.
One great fanfiction on this topic is 'The Dark Trials of Snape'. It really delves into Snape's inner turmoil as he endures Voldemort's torture. The author does an excellent job of portraying Snape's complex emotions and his unwavering loyalty to Dumbledore even in the face of such horror.
Snape might endure the punishment in stoic silence. He is a complex character and often used to hiding his true emotions. So, he could just grit his teeth and bear it, all the while plotting his revenge or a way to get out of the situation.
The possible reasons are numerous. For starters, fans might be interested in exploring the idea of how two very different characters like Snape and Hermione could be related. It could also be a way to give Hermione a more mysterious origin. Since Snape has such a complex and often misunderstood character in the original series, tying him to Hermione in this way can create interesting storylines. Additionally, it might be a form of wish - fulfillment for some fans who want to see a different kind of family structure in the Harry Potter universe.
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.
A creative reason could be a magical prank gone too far. The Marauders or some other mischievous students play a prank on Snape using a new, untested spell. The spell backfires and Snape ends up in a state where he needs to be diapered. This would lead to a story of revenge, forgiveness, or just chaos at Hogwarts.
The fact that Snape has so many secrets in the original series is a big factor. Fanfiction writers might take these secrets and turn them into evidence of his traitorous behavior. For instance, his role in the prophecy and how he dealt with it. Also, his teaching methods, which some might see as cruel, could be used as a reason to portray him as a traitor in fanfiction. This is all part of the creative exploration that fanfiction allows, to re - evaluate and re - imagine characters in new and different ways.
In some fanfictions, Snape might be working with Voldemort because he has been blackmailed. Voldemort could have found out some deep, dark secret about Snape and is forcing him to cooperate. This could be related to Snape's past or something he has done that he doesn't want to be made public.
One reason could be to add a shock factor. It completely changes the expected family relations in the original story. Another reason might be to explore Snape's character more deeply. If Harry is his son, it gives a new perspective on Snape's actions and emotions towards Harry throughout the series.