Hermione might be a common character. Since she's Harry's friend and very intelligent, she could be summoned along with Harry or find a way to follow him. Dumbledore could also make an appearance in some stories. He's very powerful and wise, so he might show up to guide Harry in the new world. Ron could be another one. His loyalty to Harry might lead him to try to rescue Harry from the other world.
In many of these fanfictions, Sirius Black could be a character. Since he has a special connection to Harry, he could somehow end up in the other world as well. Hagrid might also be there. His love for magical creatures could lead to interesting interactions in the new world. And then there are the antagonists in the new world. They could be powerful wizards or other beings that oppose Harry and his presence in their world.
Hermione would be a common character. She would likely be very determined to find Harry and bring him back. She might use her vast knowledge of magic and research skills to track him down.
Dumbledore could make an appearance in the form of a guiding spirit or through memories. His wisdom could be crucial for Harry as he navigates the new situations outside of town.
Ron could also be there. He'd bring his sense of humor and loyalty. Maybe in a story set in Australia, Ron would be the one to make friends with the local magical folk first because of his easy - going nature, and then introduce Harry to them.
Luna Lovegood might be in the fanfiction. She has a unique perspective on magic, and she could offer some interesting insights during the examination. Neville Longbottom could also be present. He's been through a lot in the wizarding world, and his presence could add another layer to the story. Additionally, some fanfictions might include characters from Snape's past, like Lily Potter. Her presence, either in flashbacks or in some magical form, could greatly affect the dynamic between Snape and Harry during the examination.
In some 'harry gets summoned to another world fanfiction', a cool plot is that Harry gets summoned to a world where magic is scarce. He has to figure out how to use his existing magic knowledge to help the people there discover or regain their magical abilities. Or perhaps he's summoned to a world where there are mythical creatures he's never seen before, like giant talking birds or shape - shifting foxes, and he has to form alliances with them to survive.
Hermione would likely be there. She is always interested in learning, so she'd be involved in any study related to magical creatures. Ron might also be around, perhaps getting into some comical situations with the creatures. Hagrid is another obvious choice, as he has a deep love and knowledge of magical creatures.
Ron could also be there. He might be a bit jealous at first if Harry's adopted family is wealthier or has more influence in the wizarding world. But later, he would support Harry as always.
Hermione would definitely be one of the main characters. She could be the one to research all about braces in the wizarding library to see if there are any magical implications or ways to make the process easier for Harry. And she would offer him lots of advice and support.
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.