Hermione and Ron are also likely to be important characters. They would be there to support Harry, try to figure out what's going on, and probably try to save Harry from this dangerous situation. Hermione with her vast knowledge of magic might be trying to find a way to break the connection between Harry and Voldemort, while Ron would be there with his loyalty and courage to stand by Harry.
Harry Potter is central as the possessed. Voldemort is crucial as the possessor. Harry's friends are bound to be main characters. Hermione, with her intelligence, would be constantly observing Harry's strange behavior and coming up with theories. Ron, being Harry's loyal friend, would be by his side and ready to fight for him. Also, characters like Sirius Black, if he's still alive in the fanfiction's timeline, could be involved. He has a close connection to Harry and would surely want to help him get rid of Voldemort's control.
The Weasley family in general would be involved. Ginny, for instance, would be heartbroken seeing Harry on Voldemort's side. The family's loyalty to Harry would be put to the test, and they would be among the main characters as they try to either bring Harry back or fight against him if he goes too far with Voldemort.
Obviously, Harry Potter and Voldemort are the main characters. Harry, who makes the unexpected choice to join Voldemort. And Voldemort, who welcomes Harry into his ranks, perhaps with an ulterior motive.
Obviously, Harry Potter and Voldemort are the main characters. But there could also be other important characters like Hermione and Ron. Hermione might be trying to understand Harry's decision and Ron could be in shock or even feel betrayed at first. Dumbledore, even in spirit form perhaps, could also play a role as he was always a guiding figure for Harry and his presence could still influence Harry's actions in this strange new situation.
Obviously, Harry Potter and Voldemort would be the main characters. Since it's about an 'evil Harry Potter', he would be a central figure with a different personality than the canon Harry. He might be cruel, power - hungry and have a disregard for the rules of the wizarding world. Voldemort, on the other hand, would be the rescuer, perhaps seeing Harry as a tool or a kindred spirit in his evil plans.
Snape could also be a character in such a fanfic. His complex relationship with both Harry and Voldemort makes him an interesting addition. He might be in a difficult position, having to keep his cover as a double - agent while also trying to find a way to save Harry without revealing his true intentions to Voldemort.
Harry Potter would likely be one of the main characters. Since Ginny is his love interest in the original series, he would surely be affected by her marriage to Voldemort. He might be the one to try and rescue her or stop the marriage. Ron Weasley, Ginny's brother, would also be important. He would be outraged and would probably be part of any plan to oppose the union.
There could also be other important characters. For instance, Hermione Granger. She would be very concerned about Harry's situation. She might try to research ways to break the betrothal using her vast knowledge of magic. Ron Weasley too would be involved, probably being more impulsive in his attempts to save Harry from this strange and dangerous situation.
Hermione would be one of the main characters. She might be very skeptical at first about Harry's new friendship with Voldemort. She would constantly be on guard and try to figure out Voldemort's true intentions. Another would be Dumbledore. He would likely be watching the situation closely, trying to guide Harry and also be prepared to deal with Voldemort if he reverts to his evil ways.
Snape could play a crucial role. Given his past with both Voldemort and his role at Hogwarts, he might be torn between his loyalty to Dumbledore's cause and his complex relationship with Harry. He could be the one who has to make a difficult decision when Harry starts to side with Voldemort. Additionally, Draco Malfoy could be involved. He might see Harry's change as an opportunity to gain more power within Voldemort's ranks, or he could be jealous of Harry's new - found position with the Dark Lord.