The main characters could include some of the new generation as well. For example, Albus Potter or Scorpius Malfoy. They could be at the center of this 'war' in the fanfic, perhaps dealing with the consequences of their parents' actions. Ginny Weasley could also be a main character, as she's a strong witch in her own right. And then there are the Hogwarts professors. Professor McGonagall could be leading the defense of Hogwarts in this war - like situation, and Professor Flitwick could be using his magical expertise to help the side he's on.
There's no way to tell without reading the fanfic. However, it might feature some of the more popular secondary characters from the Harry Potter books like Luna Lovegood or Draco Malfoy. They could be given a more central role in this fanfic, with the story revolving around their own means and ends.
Well, George Weasley could be a main character. After losing Fred, he could be trying to keep the joke shop going while also dealing with his grief in a post - war world. Cho Chang might be another main character. She could be working with international wizards to strengthen relations between different wizarding communities after the war. And Seamus Finnigan could be part of the group. He could be involved in some magical research related to how to prevent future dark wizards from rising, using his experiences from fighting in the war.
Hermione Granger would also be a crucial character. Her intelligence and vast knowledge of magic could be key in understanding the powers of the Infinity Stones and coming up with strategies to deal with them. She could also be the one to communicate with the Avengers if they come to Hogwarts, as she is good at dealing with new and complex situations.
Harry Potter is surely one of the main characters. He is the central figure in the fight against Voldemort during the second war.
Definitely the two male leads. Their competitive and comical relationship is the heart of the movie and can be explored further in fanfic. You can show more of their backstory and how they became such rivals.
You could have a new generation of witches and wizards as the main characters. For example, the children of the original trio. They might be visiting the manor for the first time and discover something that their parents had missed. There could also be a misfit wizard who finds a sense of belonging at the manor, and his story could be the focus.
In a 'harry potter inquisitor fanfic', the main characters could include the Inquisitor, who is the central figure driving the investigations. Then there could be a new character, an exchange student from a far - off magical school. This student has a different approach to magic and catches the Inquisitor's eye. Additionally, Professors Snape and McGonagall could be main characters. Snape might be secretly working against the Inquisitor if he thinks their actions are unjust, while McGonagall could be trying to keep the peace between the Inquisitor and the students. The interactions between these characters would create a rich and engaging story.
Fred and George Weasley could be the main characters in a new business adventure. Maybe they expand their joke shop business to include international locations. They could come up with new products that are suitable for different wizarding cultures. For example, they might create a line of magical fireworks that are designed to celebrate different wizarding holidays around the world. They would have to deal with the challenges of international trade in the wizarding world, like different magical regulations and cultural taboos.
In a 'Harry Potter Windsor fanfic', the main characters could include Ron Weasley. He could bring his humorous and sometimes clumsy nature to the interactions with the Windsor family. Also, an older member of the Windsor family, like the Queen (in a fictional magical version), could be a main character. She could be the one who is initially skeptical but then comes to accept the existence of magic. And Dumbledore could play a role as the wise guide in any magical matters involving the Windsors.
Hermione Granger could also be a main character. With her intelligence, she would be quick to learn ninja techniques and could even help improve them with her knowledge of magic. She might study the ancient ninja scrolls and find ways to combine the knowledge of both worlds for the greater good.