Well, the themes can vary. But often you'll see the theme of transformation. Harry's change into a submissive vampire is a big part of it. Then there's the theme of acceptance. He has to accept his new role and status in the vampire world. Also, a lot of these fanfics might have a theme of loyalty, whether it's his loyalty to his new vampire 'family' or to his old friends in a different way.
One common theme is the exploration of power dynamics. Since Harry is submissive, it often shows how he interacts with more dominant vampire characters. Another theme could be identity. Harry has to figure out who he is now as a submissive vampire. And there's also the theme of relationships, like how he forms bonds with other vampires or characters from his previous life.
One common theme is the exploration of power dynamics. Since Harry is submissive, there's often a play between his vulnerability and the power of the vampires around him.
One common theme is the struggle with identity. Harry has to figure out who he is as a vampire in addition to being a wizard. Another theme is the isolation. Vampires are often solitary creatures, and Harry may experience this in these fanfics. Also, the power aspect is there. His new vampire powers and how he uses or misuses them.
One common theme is the exploration of power dynamics in relationships. For example, a female character might be submissive to a more powerful male wizard. Another theme could be the female character sacrificing her own desires for the sake of the relationship or the greater good within the wizarding world. Also, there may be themes related to loyalty and devotion in a submissive way, like a female character always following and supporting a male character's decisions without question.
The themes can vary widely. Some fanfics might focus on the mystery aspect. For example, exploring the secrets of the vampire world that Severus inhabits and how Harry gets drawn into it. Another theme could be redemption. Maybe Severus, through his relationship with Harry, is seeking some form of redemption for his past actions in the 'Harry Potter' canon. There's also the theme of survival, as both characters may face threats due to Severus' vampire nature.
Love and obsession are also common. The submissive male often becomes obsessed with the vampire seductress, while she may or may not truly love him in return. It can be a twisted form of love, as she may be using him for her own purposes, like blood or companionship. And the theme of transformation is there too. Sometimes the male may be on the verge of becoming a vampire himself, which adds another layer to their relationship.
One common theme is the struggle between her human side and vampire side. For example, she might resist the urge to drink blood because of her human values. Another theme could be isolation. Since she is now different, she might feel alone even among her friends at Hogwarts.
One common theme is the struggle between the wizarding world and the vampire world. Since Harry is from the wizarding world and the OC is a vampire, there's often a clash of cultures and rules. Another theme is the idea of forbidden love. Vampires are often seen as outcasts in the wizarding world, so a relationship between Harry and a male vampire OC is usually frowned upon.
One popular 'Harry is a submissive vampire' fanfic could be 'The Vampire's Submissive'. It has an interesting plot that delves into the unique relationship dynamics. Another might be 'Harry's Vampire Bond' which focuses on how Harry adjusts to his new vampiric nature and his submissive role within the vampire community. There's also 'Submissive Harry in the Vampire Realm' that offers a different take on the concept with a lot of character development.
One common element is the power dynamic. Often, there will be a clear contrast between the more powerful wizards and the submissive creatures. For example, in stories about house - elves, the wizards are in a position of authority. Another element is the sense of loyalty. Submissive creatures are usually depicted as being extremely loyal to their masters or the wizarding world in general. They might be willing to sacrifice themselves for the greater good of the wizards.
Friendship is also a common theme, which is very much in line with the MLP universe. Even in the presence of vampires, the fanfics often show how the characters try to maintain or build friendships. It could be a vampire making friends with ponies despite their differences, or ponies trying to befriend a vampire in order to save them from their vampiric ways. This theme of friendship often drives the plot forward and gives a positive message in these often - darker - themed fanfics.