Maybe Draco is jealous of Harry's popularity and power. Turning him into a vampire could be a way to strip him of his status among the wizarding community. Vampires are often feared and shunned, so Draco might think this would be a good way to get back at Harry.
When Draco turns Harry into a vampire, it throws his friendships into chaos. His friends are used to the regular Harry, the one who battles Voldemort and plays Quidditch. Now, he has different needs and behaviors. Some friends may distance themselves out of fear. But others, like Neville, might be curious and try to help him adjust. His relationship with Ginny would also be tested as he has to deal with his new vampire nature and how it affects their relationship.
In a 'Harry turns into a vampire' fanfiction, the story could start with Harry being cursed by a powerful and ancient spell that turns him into a vampire. His friends at Hogwarts are initially scared and unsure how to deal with him. However, Harry is determined to find a way to reverse the transformation. Along the way, he discovers that there are some positive aspects to being a vampire, such as heightened senses that help him in his detective - like investigations into the origin of the curse.
It could be a powerful vampire clan that doesn't want Harry, a new vampire, to disrupt their ways. They might try to either kill him or force him to join their ranks against his will. They could see him as an outsider who doesn't belong in the vampire world and a potential danger to their secrecy.
Well, in 'harry x draco vampire fanfiction', a frequent theme is power dynamics. As a vampire, Draco might have certain powers that change the balance in his relationship with Harry. Another is the exploration of the unknown. Vampirism is something new and different in the Harry Potter universe, so the stories often explore how Harry and Draco deal with this unknown element. And of course, there's the theme of loyalty. Their loyalty to each other is tested as they face the challenges of Draco being a vampire.
A sense of mystery and the unknown is a big part of it. Vampires are associated with mystery, and in these fanfics, that mystery is often transferred to the relationship between Draco and Harry. How did Draco become a vampire? What are the rules and secrets of his vampiric existence? And how does Harry deal with all these new elements? These are all questions that the fanfictions might explore, making the overall theme of mystery a significant part of the genre.
There's also 'Harry and the Vampire Prince'. This one stands out because it shows how the wizarding society reacts to Draco being a vampire and his relationship with Harry. It has a unique plot where they have to face many challenges together, both from within Hogwarts and from the outside magical community. It's a story that really makes you think about acceptance and love in a different context.
Obviously, Harry Potter himself would be the central character as he is the one undergoing the transformation into a born vampire. His friends like Hermione and Ron would also be important characters. They would likely play a role in either helping Harry adjust or being conflicted about his new state.
One possible plotline could be Harry struggling to control his new vampire instincts while still trying to protect his friends at Hogwarts. He might have to deal with the thirst for blood while attending classes and facing off against the Dark Arts. Another could be that he discovers a whole new vampire community within the wizarding world that has its own rules and power structures.
Well, if Snape turns Harry into a vampire in fanfiction, it would completely change the dynamic. Harry would have to deal with new instincts like the thirst for blood. His relationships would be strained as his friends might be scared of him. Also, his role as the 'Chosen One' would be redefined as he's now a different kind of being with different needs and abilities. He might have to struggle between his human side and his new vampire nature.