There could be new characters as well. For instance, a mysterious wizard or witch who Harry meets during his journey. This character could have their own motives and secrets. They might help Harry on his way, or they could initially seem friendly but later turn out to be a threat. Maybe they are related to an ancient magical bloodline that has a connection to Harry's journey.
Obviously, Harry Potter himself is a common character. His friends like Hermione Granger and Ron Weasley also often show up. They might accompany Harry on his journey or play important roles in the events that occur during his travels.
In 'harry potter reincarnated fanfiction', Voldemort can be a recurring character. If Harry is reincarnated, Voldemort might sense a strange new threat or an opportunity. Snape could also be there. His complex relationship with Harry could be re - explored in these new incarnations. And of course, Luna Lovegood might make an appearance, with her unique perspective adding an interesting element to the story.
Well, aside from the main trio, characters like Luna Lovegood are quite common. She might offer her unique insights to Harry in his new role. Also, the Weasley family members, especially Ginny, could play important parts. And of course, many fanfictions include the Hogwarts professors such as Flitwick and Sprout, who interact with Harry in different ways as he takes on the role of Hogwarts master.
Neville Longbottom might be a key character in some fanfictions. He could be working closely with Harry in reforming the Herbology department or be involved in some sort of magical conservation efforts. Luna Lovegood could also be present, maybe running an alternative magical theory research department at the Ministry. And of course, some of the old Ministry employees like Kingsley Shacklebolt might still be around, helping Harry in his new role.
Hermione Granger often appears. Since she is Harry's best friend in the original series, she can play an important role in helping Harry understand the new alternate universe. Ron Weasley is also common. His loyalty and humor can add interesting elements to the story. Dumbledore might also show up. His wisdom can be crucial in guiding Harry in the strange new world.
Hermione would probably be one of the common characters. She could be helping Harry in his research, using her vast knowledge to find solutions to difficult medical cases. Maybe she'd be working on developing new potions for healing.
Hermione would likely be there. She's Harry's best friend and would not let him be in juvie alone. She'd probably be trying to find a way to get him out legally, researching all the laws and loopholes. Ron might also show up, being another one of Harry's closest friends. He could be the more impulsive one, thinking about breaking Harry out rather than going through the proper channels. Dumbledore might also be involved in some way. He has always been a guiding figure for Harry, so he could be working behind the scenes to ensure Harry's safety and find a way to clear his name.
Hermione is often present. She might help Harry understand the legal and political implications of his new lordship. Ron would also be there, probably as Harry's loyal friend, providing support and some comic relief. Dumbledore could still play a role, perhaps as a mentor guiding Harry in how to use his new power for the greater good.
Voldemort or his followers could also be relevant in some stories. Maybe Harry is leaving because he fears a resurgence of Voldemort's forces and wants to find a way to defeat them from afar. Or perhaps some of Voldemort's old followers are still after him, and his leaving is a way to draw them away from the innocent people in Britain.
Obviously, Harry himself is a common character. Hermione is also often included as she is Harry's closest friend and very intelligent, so she can help Harry figure out how to navigate the past. Ron might be there too, providing some comic relief and loyalty. Dumbledore usually makes an appearance as he has a lot of knowledge and can offer guidance to Harry in the past.
Harry is the central figure for sure. Neville Longbottom could play a role. He might be one of the few who know where Harry is hiding and is trying to protect the trunk from being discovered. Hagrid could also be involved. He might bring Harry some food and supplies while he's in the trunk. And there could be some mysterious old wizard or witch who has some connection to the trunk and its magic.