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.
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.
Hermione could be a main character. She might be trying to find a way to rescue Harry from the timeout situation. Ron could also be there, supporting Hermione in her efforts.
Hermione is often a very popular character. She can bring her intelligence and magic skills to help Harry in new and interesting ways in the fanfiction world. For instance, she might come up with a unique spell to counter Voldemort's dark magic.
In many of these fanfictions, the Marauders (James, Sirius, Remus, and Peter) are quite popular. They were friends of Harry's parents and their presence in a time - travel story can bring a sense of nostalgia and also add a lot of action and adventure. Bellatrix Lestrange can also be a prominent character on Voldemort's side. Her fanatical loyalty to Voldemort and her dark magic skills can make for some intense and exciting scenes, especially when she clashes with the heroes in different time periods.
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.
Hermione is often a popular character. She might play a role in helping Harry understand the implications of Voldemort's reincarnation, using her vast knowledge of magic and history.
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.
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.
Ron would also be important. His loyalty to Harry is unwavering. He might be the one who bravely volunteers to go on the most dangerous part of the rescue mission, perhaps facing off against some of Voldemort's most feared Death Eaters.
One possible plotline could be Harry being held captive in one of Voldemort's dark lairs. Voldemort might use the Cruciatus Curse on him repeatedly to try and break his spirit or get information about the Order of the Phoenix. Harry could be isolated and tortured while his friends desperately search for him.