Dumbledore, if he were still alive, would be very cautious. He would try to guide Harry towards using his powers for good, or at least in a way that doesn't disrupt the balance of the wizarding world. The other Hogwarts professors would likely be split. Some would be horrified and want to expel Harry, while others would see it as an opportunity to study a rare form of magic and its implications.
The teachers at Hogwarts, like Dumbledore (if he were still alive in the fanfic), would be deeply concerned. Dumbledore always saw great potential in Harry for good. He would probably try to understand what led Harry to this path and would use all his wisdom and magic to try and turn Harry back. The other teachers would also be on high alert, fearing for the safety of the students and the future of the wizarding world.
Hermione would be devastated. She has always been Harry's loyal friend and believed in the fight against the Dark Lord. She would probably try to convince Harry to come back to the right side, reasoning with him about the evil nature of the Dark Lord's actions. Ron, on the other hand, would be both angry and confused. He might initially think it's some sort of joke or that Harry has been tricked.
Harry Potter would likely be on high alert immediately. He has experience with fighting Dark Lords, so he would start gathering his old friends and allies. Hermione would be researching like mad, trying to find any weaknesses of this new Dark Lord. Ron would be a bit more hesitant at first but would soon join the fight. The younger generation, like Ginny and Neville's students, would be both scared and determined to prove themselves in the face of this new threat.
Ron would be devastated. He's been their best friend for years. He'd probably try to talk them out of it at first. If that fails, he might have to choose between loyalty to his friends and what he believes is right. The Hogwarts professors, like Dumbledore (if he were still alive in the fanfiction), would be very concerned. Dumbledore would likely see it as a great loss of two of the brightest lights in the wizarding world. He might try to find a way to reverse whatever led them down this dark path.
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 professors at Hogwarts would have different reactions. Professor Snape might be secretly intrigued by this new and strange creature while outwardly showing disdain. Professor McGonagall would be concerned for the safety of the students and would start organizing protection spells around the school. Hagrid, being the lover of strange creatures, might try to approach it in a friendly way at first, until he realizes how dangerous it is.
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.