It's a really odd concept. Snape and Harry have a very specific relationship in the Potter universe. Snape was Harry's teacher and had a lot of his own backstory tied to Harry's parents. Cheating implies a romantic or unfaithful relationship which doesn't make sense in the context of their relationship in the books.
Well, sometimes authors want to create a shock factor. By having Snape take advantage of Hermione, it would be a very unexpected and controversial plot twist. Also, it could be due to a lack of understanding of the characters' personalities. Snape is a proud and somewhat noble character in his own way, and Hermione is not a weakling. So this idea might come from not fully grasping their essence.
Well, he might be quite reluctant at first. Snape has always had a rather complex relationship with Harry. He might see it as a huge burden and be full of doubts. After all, he has his own grudges and past issues with James Potter, Harry's father. But on the other hand, he also has a sense of duty towards Harry as he was Lily's son. So it's a mix of emotions that he has to deal with.
People like it because it's a complete role - reversal. Snape, who was often seen as a rather cold and strict character in the original story, becomes a nurturing figure. It's an interesting exploration of his character's hidden depths.
The author can focus on Snape's actions towards Hermione in the context of the Hogwarts environment. For example, his snide remarks during potions class could be made more cutting and frequent, gradually wearing on Hermione's confidence and causing her trauma.
This is an inappropriate concept. In the Harry Potter series, Snape has his own role and relationship with Harry. He is often a figure of mystery and conflict towards Harry. The idea of such a non - consensual and inappropriate relationship is not only against the ethics of the story but also offensive to many fans who love the series for its positive values.
I think it's a rather dark and unfaithful take on the characters. In the original Harry Potter lore, Lily was in love with James. However, fanfiction is all about exploring different possibilities, but this one might not sit well with a lot of fans who have a more traditional view of the relationships.
One way it could work is through a complex backstory. Maybe Snape had a relationship before he became so deeply involved in the wizarding war. He could have met Bella's mother, and for some reason, Bella was raised away from him. In the fanfic, Snape could discover her true identity later. This would add a whole new layer of drama, as Snape is a very complex character with his own loyalties and secrets. And Bella, being a Muggle - born in the original story, this would change her entire backstory and connection to the wizarding world.
Some fanfictions show Snape using Occlumency lessons as a way to bully Harry. He might use his superior skills to intimidate Harry, making him feel small and incompetent. For example, he could make snide remarks while invading Harry's mind, which is a form of mental abuse.
It's a rather strange and inappropriate idea. Harry and Snape have a complex relationship in the original series, and this concept distorts that relationship in an unseemly way. Fanfiction should enhance the world of the original work, not introduce such out - of - place and improper scenarios.