Maybe it's a strict pure - blood supremacist. They see Hermione, a Muggle - born, in a relationship with Snape and decide to oppose it. They could try to use their influence in the wizarding world to create obstacles for the two, like getting Snape fired from his teaching position or expelling Hermione from Hogwarts.
It could be a dark wizard who is jealous of Snape's relationship with Hermione. This antagonist might try to break them apart by causing trouble in Hogwarts or spreading false rumors about them.
Another possibility is a dark wizard or a group of dark wizards who are after some powerful magic that the Lestrange family has, and Hermione gets in their way as she tries to protect the family or uncover the secrets. They would be the main force that Hermione has to face and overcome throughout the fanfiction.
Perhaps a powerful magical being from a different realm is the antagonist. This being might mistake Hermione for someone else or see her as a key to something in the wizarding world. So, it uses its magic to make her disappear. This being would be very difficult to defeat or negotiate with, making it a huge challenge for those trying to find Hermione.
It could be a dark wizard who discovers Hermione's hidden identity and wants to use it for his own evil purposes. Maybe he wants to harness the power that comes with her true identity to take over the wizarding world.
Yes, there might be some fanfictions that handle this scenario in a non - inappropriate way. Some writers may explore complex relationships or emotional moments between the characters in a more platonic or emotionally charged context that doesn't cross into inappropriate territory. However, it can be quite difficult to find among the vast sea of fanfiction, as the idea can be easily misinterpreted or taken in the wrong direction.
One possible scenario could be a moment of intense conversation where Hermione is sitting in Snape's lap and they are having a deep discussion about magic theory that only they understand. It might be a turning point in their relationship in the fanfiction world.
It could be a power - hungry student who wants to undermine Hermione and Favo Prefect. This student might be jealous of their status as prefects and the respect they get from teachers and students alike. So, they try to create problems for them, like spreading false rumors or sabotaging their projects.
It could be an old and powerful vampire who sees Hermione as a threat to his rule. Since Hermione is a very intelligent witch - now vampire - she might be able to figure out a way to undermine his power.
It could be an old muggle acquaintance who is jealous of Hermione's success in the wizarding world. Maybe they sense that she's different and are determined to find out her secrets and expose her.
It could be the same group or person who tortured her in the first place. They might be trying to finish the job or silence her before she can expose their evil deeds.
Hades would be a likely main antagonist. He rules the Underworld and might see Hermione as a threat or an opportunity. If he thinks she has something valuable, like her knowledge of magic, he could try to keep her trapped in the Underworld. Or he might oppose her if she's trying to change something in his domain that he doesn't want changed.