Ron might be initially shocked and a bit awkward around Harry. But being a good friend, he would eventually come around and try to support Harry, perhaps with some clumsy attempts at humor to lighten the situation.
Hermione would probably be very curious and immediately start researching ways to reverse the transformation or at least understand it better. She'd be quite protective of Harry too.
Hermione would probably be initially shocked but then would be very curious about the magical properties that might have caused the transformation. Ron, on the other hand, would likely tease Harry at first but would soon come to accept it and see it as just another strange thing in the wizarding world.
The characters' reactions would be diverse. Harry, being the main character, would likely feel a great sense of responsibility. He'd have to face the judgment of both the wizarding community and the vampires. Hermione would be her usual studious self, looking for any precedents or magical knowledge to help. Ron would probably voice his concerns loudly, thinking it's a dangerous and strange situation. The vampire involved would have her own emotions, perhaps a mix of fear and hope for the future. And other vampires in the community could range from being supportive to being hostile depending on their beliefs and positions within the vampire hierarchy.
Hermione, on the other hand, would likely have a more critical view. She'd analyze the fanfictions for their accuracy in terms of magic lore and Hogwarts traditions. If there were any inaccuracies, she'd be quite perturbed. However, she might also appreciate the creativity that goes into some of the well - written ones that add new dimensions to their magical world.
The Death Eaters and their sympathizers would be terrified. Harry, as the overlord, would be a major threat to their ideology. Voldemort, if he somehow still existed in this fanfiction, would be in direct opposition to Harry. However, some of the more neutral characters, like Luna, would probably see Harry's new role as an opportunity for positive change in the wizarding world and would be happy to support him in his endeavors.
Well, if Harry turns into a cat, Hagrid would be quite worried. He might try to take care of Harry in his cat form, giving him treats and a warm place to sleep. The other students would have a mix of reactions. Some might be scared, thinking it's some sort of dark magic at work. But his closer friends like Neville would be determined to help. Neville might even try some of his own plant - based magic to see if it could help Harry turn back. Snape, of course, would probably be skeptical and think Harry got himself into this mess on purpose.
Hermione would probably be very curious. She'd immediately start researching in the library to find out if there are any known cases of wizards having tails and how to reverse it if it was an unwanted condition. Ron, on the other hand, would likely make some jokes at first, but then be supportive. He might say something like 'Well, at least it makes you stand out even more, Harry!'. Dumbledore would be his usual calm self. He might see it as a sign of something greater or a test for Harry, and offer some cryptic advice.
Hermione would probably be both curious and worried. She'd want to research all about Harry's half - demon nature to find out what it means and how to help him. Ron, on the other hand, might be a bit more hesitant at first. He might be a bit scared but would eventually come around because of his loyalty to Harry.
He could be shocked. Maybe there are some fanfictions that take a very dark turn or have unexpected pairings that he never thought of. He'd probably need some time to process such strange ideas. And he might also be curious to see how far the creativity of the fans can go. He might even get some new ideas about his own life from reading some of the more imaginative fanfictions.
Some characters might be excited. They could see him as a new source of knowledge and magic.
The Weasley family would have different responses. Mrs. Weasley would be motherly and concerned about this strange new person. Fred and George would see her as a source of new ideas for their pranks and inventions. Ginny would look up to her as a strong female figure, much like she does with Hermione. And all of them together would gradually get used to having Powergirl around, and they would all grow from the experience of interacting with someone from a completely different world.