One common theme is the loss of humanity. When a character is turned into a vampire, they often have to grapple with losing their human emotions and values. Another theme is the power struggle. Newly - turned vampires usually have to figure out their place in the vampire hierarchy.
One popular vampire turning fanfiction is 'The Crimson Embrace'. It tells a story of a young girl who gets turned into a vampire in a very mysterious and alluring way. The author does a great job of describing the transformation process and the new world she enters.
Jealousy could be one motive. Maybe Katherine is jealous of Elena's popularity and relationships, so she turns her into a vampire to make her life as difficult as hers. Another motive could be power. By turning Elena, Katherine might be trying to gain some sort of control over her or use her for her own plans.
One possible plotline could be that Sonic gets bitten by a vampire during one of his adventures in a spooky zone. He then starts to notice changes in himself, like a craving for blood and enhanced speed at night. His friends initially don't realize what's wrong and think he's just acting strange. As he turns more vampiric, he has to struggle with his new nature and not harm his friends.
Snape could be motivated by some dark magic experiment. He might have thought that turning Harry into a vampire could unlock some hidden power that could be used against Voldemort or for his own gain in the wizarding world politics.
One interesting plot twist could be that Peter's spider - sense is affected by his new vampire nature. Instead of warning him of physical danger, it now warns him of approaching sunlight or the presence of vampire hunters. Another could be that his relationships with his friends and family change drastically. For example, he has to hide his new identity from Aunt May, but she starts to suspect something when he avoids going out during the day. Also, his friendship with Ned might be strained as he has to keep this huge secret.
Well, his strength could increase even more. Vampires are often depicted as having superhuman strength, and combined with Peter's existing spider - strength, he could become incredibly powerful. His speed might also be enhanced, allowing him to move faster than ever. And his ability to climb walls could potentially be altered. Maybe instead of using his spider - like grip, he could now scale walls more like a vampire, using his newfound agility and grace.
One possible plotline could be that Henry Lau, after turning into a vampire, struggles to come to terms with his new identity. He might try to hide it from his friends and family at first. For example, he could be a famous musician in his human life, and now he has to find ways to continue his career without revealing his vampiric nature. He may have cravings for blood that he tries to resist, leading to internal conflicts.
The exploration of the Pokemon - vampire relationship. How do other Pokemon react to those that have been turned? And how do trainers deal with their once - friendly Pokemon now having a thirst for blood? This creates a whole new set of storylines and character interactions within the fanfic.
I'm not sure there are a lot of such specific fanfictions, but you could start by looking on major fanfiction platforms like Archive of Our Own. Try searching for the exact phrase 'Harry turned vampire Snape mate' in the search bar. There might be some hidden gems there.