Dumbledore is an important character in these fanfictions. His actions and secrets play a huge role in Harry's decision - making. If Harry discovers some of Dumbledore's darker secrets, it could be a reason for him to switch sides. Additionally, characters like Sirius Black can be involved. If Sirius were still alive in the fanfiction, his relationship with Harry could be a factor. If Harry believes that Sirius's death was somehow the fault of the 'light side', he might be more inclined to switch.
Obviously, Harry Potter himself is the central character as the title implies. Voldemort is also often involved as the main figure on the 'dark side' that Harry might switch to or interact with differently. Then there's Snape. His complex relationship with Harry could be a key factor in the story. In some fanfictions, he might be the one who either tempts Harry to switch sides or tries to prevent it depending on his own motives.
Hermione and Ron are common characters in 'Harry Potter Switches Sides' fanfiction. Hermione might be the voice of reason trying to bring Harry back if he switches, or she could also be convinced by Harry's new perspective. Ron, on the other hand, could be the one who feels the most betrayed if Harry changes sides. Bellatrix Lestrange is also often included. She could be the one who tries to manipulate Harry into joining Voldemort's side or be an obstacle for Harry if he tries to return to the 'light side' after a brief stint on the 'dark side'.
Obviously, Harry Potter himself is the central character as the story revolves around his switching sides. Hermione and Ron also play significant roles. When Harry starts to show signs of siding with the dark side, Hermione might try to use her intelligence to figure out what's wrong and bring him back. Ron, on the other hand, could be more impulsive in his reactions, either trying to fight Harry if he becomes a threat or trying to persuade him to return to the good side.
Obviously, Harry Potter himself is the central character in this type of fanfiction. Then there are often characters like Voldemort or his Death Eaters, as they are the ones Harry would be changing sides to. Bellatrix Lestrange could be a key figure in trying to persuade Harry or manipulate him into joining their side.
One interesting scenario could be Harry realizing that the so - called 'dark side' has been misrepresented. Maybe he discovers that the Death Eaters have some valid grievances against the Ministry's corruption, which makes him question his allegiance. Another could be that he's influenced by a powerful dark magic artifact that makes him see things from Voldemort's perspective, at least temporarily.
Another plotline could involve Harry being betrayed by the Order of the Phoenix. Feeling hurt and lost, he decides to side with Voldemort out of revenge. However, as he gets closer to the dark side, he realizes that Voldemort's true nature is far more evil than he thought and has a change of heart.
Hermione Granger is also a common character. Given her love for knowledge and her skills in magic, she would likely be researching the best spells and magical theories to make the terraforming successful. She might be the one to find ancient spells that are crucial for the process.
In many expelled Harry Potter fanfictions, the Weasley family as a whole gets involved. Molly Weasley would be worried sick about Harry and would be cooking up plans to get him back. Fred and George might use their prank - making skills to expose the truth behind the expulsion. Ginny, being Harry's love interest in the original series, would be actively involved in trying to clear his name. And don't forget about the Hogwarts professors. McGonagall would probably be torn between following the rules and believing in Harry.
Harry Potter himself is often a central character. He might be shopping for new school supplies at Flourish and Blotts or looking for a new broomstick at Quality Quidditch Supplies. His friends, like Hermione and Ron, usually accompany him. Hermione might be more interested in books and rare magical artifacts, while Ron would be eyeing the latest Quidditch gear.
Mrs. Weasley is a very likely character. She's an expert at cooking and baking in the normal wizarding world, so in fanfiction about magical bakes, she could be teaching the younger characters how to make special bakes. Hagrid might also be involved. He could bring in some really strange ingredients from the Forbidden Forest, like giant acorns, to be used in the bakes.
Hermione Granger is often involved. In some fanfictions, she discovers hidden conspiracies within the Hogwarts library. For example, she might find a book that reveals a plot by some of the older pure - blood families to keep certain magical knowledge from half - bloods and Muggle - borns.
Harry Potter would surely be one of the key characters. His relationship with Draco, which has always been a mix of rivalry and grudging respect, could play a huge role. As Draco switches sides, Harry would be initially suspicious but then come to accept and work with him. Hermione Granger is also likely to be important. Her intelligence and strong moral compass could influence Draco further and she could be the one to first recognize his change of heart.