Well, perhaps a plot twist could be that Hermione turns into a vampire but discovers that there are different 'types' of vampires in the fanfiction world. She might be a special kind of vampire that has the ability to walk in sunlight without harm. This would set her apart from other vampires and cause a stir in the vampire community. She could then use this unique trait to broker peace between the vampires and the wizarding world, which has always been at odds with the vampire kind.
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 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 when Natsu turns into a dragon, he loses his memory of his human friends. This would create a lot of drama as his friends try to bring back the Natsu they know. Another could be that he turns into a different kind of dragon than expected, perhaps one with a very rare and powerful ability that attracts the wrong kind of attention from dark forces in the fanfiction world. And also, he might transform into a dragon at a crucial moment during a battle, not only surprising his enemies but also his allies, changing the whole dynamic of the fight.
Maybe a plot twist could be that Sam's transformation into a kid is part of a larger, more sinister plan by an unknown entity. This entity could be using Sam as a child to manipulate Dean in some way, perhaps by making Dean over - protective and leading him into a trap.
A great plot twist could be that Percy's transformation into a woman is not just a physical one but also gives her new powers or a different connection to the gods. Maybe she can now communicate with a goddess in a way that male Percy couldn't, and this new connection helps her on her quests in ways that are unexpected and exciting.
A possible plot twist could be that Hermione is a half - veela. This is not related to being a Muggleborn at all. The fanfiction could show how her veela heritage affects her magic and her relationships at Hogwarts. For example, it might make her more alluring and powerful in certain types of magic, like charms. This would completely change the way her character is typically portrayed in the original stories where she was thought to be a Muggleborn.
One interesting plot twist could be that Hermione discovers she has a long - lost royal relative. This throws her into the world of royalty where she has to learn the complex rules and etiquettes. She might initially struggle but then use her intelligence, like in the Harry Potter series, to navigate through palace politics and rivalries.
One interesting plot twist could be that Hermione, as a Gryffindor in the original series, starts to question the values of her own house because of her newfound admiration for Slytherin. Maybe she discovers a long - lost family connection to a Slytherin family, which makes her more empathetic towards their ways. Another could be that she uses Slytherin - like cunning to solve a problem that Gryffindor bravado couldn't handle, causing a rift between her and some of her Gryffindor friends.
Well, one interesting plot twist could be that Hermione discovers she has a hidden connection to the Muggle Princess world that changes her perspective on magic. Maybe she finds out that her family has a long - lost heritage in the Muggle Princess realm and this knowledge makes her question her place in the wizarding world.
One interesting plot twist could be that Draco saves Hermione not out of pure altruism but because he discovers a dark plot against the wizarding world that Hermione unknowingly holds the key to solving. So, by saving her, he's also saving himself and his family from a greater threat.
One interesting plot twist could be that Hermione's real family is a powerful wizarding dynasty in hiding. For example, they might have been in hiding from a dark wizard who was after their unique magical abilities. Another could be that she was adopted to protect her from a prophecy related to her future powers. Maybe she discovers that she has a connection to an ancient magical artifact that only her real family knew about, and this discovery changes her whole perspective on her identity and place in the wizarding world.