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.
In such a fanfic, perhaps Harry Potter is magically manipulated. The Dark Lord could use some powerful dark magic to cloud Harry's judgment. Harry might then start to use his skills and knowledge, which were originally meant for good, to help the Dark Lord's evil plans. For example, he could use his Parseltongue ability to communicate with dark creatures for the Dark Lord's purposes.
The Order of the Phoenix would see Harry's joining of the Death Eaters as a major setback. They would likely view it as a sign that Voldemort has become even more powerful. Dumbledore, if he were still alive, would be very concerned and would try to understand what led Harry to this decision. He would also be devising a plan to get Harry out of the clutches of the Death Eaters.
Dumbledore could be seen as the main antagonist from Harry's new perspective on the dark side. Dumbledore represents all that is good in the wizarding world, and if Harry has turned to the dark, Dumbledore would be the one trying to stop him, to bring him back to the light. So in this context, Dumbledore becomes the opposition that Harry has to face.
There could be the leader of the coven. This person might be an old and powerful witch or wizard who has been in the coven for a long time. They would be the one to guide Harry into the ways of the coven.
Well, one possibility could be that Harry, feeling betrayed by the Order of Phoenix or perhaps influenced by some dark magic artifact, starts to question the motives of the good side. He might see how the Dark side offers power and a different kind of 'freedom'. For example, Voldemort could manipulate Harry by showing him how the wizarding world could be united under his rule, eliminating the in - fighting among pure - bloods, half - bloods and Muggle - borns, though of course this would be a false promise.
Well, one possibility is that Harry is tricked into joining the dark side. Maybe Voldemort uses some dark magic to cloud Harry's mind and make him believe that the dark ways are the right ones. He could start using dark spells and turn against his friends.
If Harry Potter joins the dark side in fanfiction, it would completely颠覆 the original story. His friends would become his enemies, and Hogwarts would be in chaos. The power dynamics in the wizarding world would shift, and Voldemort might see Harry as a valuable ally or a potential threat to his own leadership. It's a very interesting concept to explore in fanfiction.
The Death Eaters would initially be overjoyed. They would think that with Harry on their side, they are invincible. But some of them might also be suspicious of Harry's motives, fearing that he is a double - agent. As for the general wizarding population, they would be terrified. Harry was seen as their hope, and now that he has joined Voldemort, they would feel completely hopeless and defenseless.
Hermione would likely be one of his allies. She's intelligent and has a strong sense of justice, always having been interested in the rights and wrongs of the wizarding laws. She could provide Harry with valuable research and advice.