One interesting twist could be that the vampire breath actually transfers the consciousness of the victim into the body of a vampire for a short time. This leads to a situation where the main character experiences life as a vampire and discovers that vampires are not all bad, which completely changes their perspective on the vampire - human conflict.
One idea could be a story where the main character discovers that the vampire breath has a special power. For example, it can freeze time for a short period, and they use this to their advantage to outwit the vampires.
One interesting plot twist could be that Buffy becomes a vampire but still retains some of her Slayer powers. This creates an internal struggle as she has to fight her new vampire instincts while also using her old skills. Another could be that she turns into a vampire and finds out that there's a whole new level of vampire society that she was unaware of, which changes her perspective on the whole vampire - slayer dynamic.
One interesting plot twist could be that Hermione, as a vampire, still retains her thirst for knowledge. Instead of blood, she discovers a way to feed on knowledge energy. For example, she might visit ancient libraries at night and absorb the knowledge stored in the books, which gives her a different kind of 'nourishment'. Another plot twist could be her relationship with her friends. Harry and Ron might initially be scared of her, but then they realize that she's still the same Hermione deep down. They could then team up to fight against vampire hunters who see Hermione as a threat just because of what she's become.
One interesting plot twist in 'Naruto: A Link to the Wild' is that Naruto's shadow clones start to develop their own consciousness based on the different environments in Hyrule. This creates a whole new set of challenges for Naruto. In 'Wild Naruto', a plot twist could be that the Koroks in Breath of the Wild are actually the descendants of a lost shinobi tribe. It's a really strange and fascinating connection. And in 'The Hybrid World of Naruto and Breath of the Wild', there's a plot twist where the two main characters from each universe, Naruto and Link, have to swap their powers to defeat an ultimate enemy that can only be defeated by using the other's abilities.
One interesting plot twist could be when Naruto, as a vampire, discovers a hidden power within himself that is related to the Rosario Vampire lore in a completely unexpected way. Maybe it's a power that only activates when he's in the Rosario Vampire world and it changes the course of the story.
A really unique plot twist in DC Vampire fanfiction can be that the Green Lantern Corps has to deal with a vampire - like entity that feeds on the energy of their rings. This forces them to find new ways to power their rings and fight this entity. And sometimes, a plot twist is that a vampire version of Aquaman rules the underwater world, and the normal Aquaman has to figure out how to stop him without getting turned into a vampire himself.
One interesting plot twist could be that Dracula is actually D's long - lost father. This would completely change the dynamic between the two and add a whole new layer of conflict. D, who has been hunting vampires all his life, would be forced to reevaluate his actions.
One interesting plot twist could be that the father of Caroline's baby is a long - lost relative of an original vampire. This would bring in a whole new level of drama as different vampire factions might try to either protect or harm Caroline and her unborn child depending on their own motives.
One interesting plot twist could be that Bella's transformation into a vampire gives her a unique power that no other vampire has. For example, she might be able to control the weather. Another twist could be that instead of joining the Cullen family right away, she runs off on her own to explore the vampire world. Maybe she discovers a whole new coven that has different values and ways of life compared to the Cullens.
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.