Hermione is often one of the main supporters. Her intelligence and knowledge of magic are always at Harry's disposal. She can help him research spells and strategies when he takes charge of a situation.
Ron is also there by his side. Ron's loyalty and his ability to lighten the mood in tough situations are valuable. He might be the one who encourages Harry when others doubt his leadership decisions.
His friends like Ron and Hermione would surely support him. They have been through a lot together, and they believe in Harry's leadership. Also, the Weasley family in general would be behind him. They have always been on Harry's side in his battles against the dark forces.
Some of the younger students who looked up to Harry, like Neville, could support him. Neville has grown to be a strong and brave character. He might see Harry's actions as a way to make the wizarding world a better place. Also, those students who have felt wronged by Dumbledore's decisions in the past, perhaps in terms of school policies or safety, could come forward to support Harry in the court case.
Hermione Granger would surely be one of the first to support him. She's always been by his side, helping him with research and providing intelligent advice. Ron Weasley would also be there, being Harry's loyal friend through thick and thin. Neville Longbottom could be another supporter. He's grown into a brave and capable wizard, and he would stand with Harry in his new role. Dumbledore, if he were still alive in the fanfiction, would likely offer his wisdom and guidance to Harry as he takes on this new and important role.
Ron would also be there. He might start out a bit reluctant, but then get into it. He could be Harry's partner in physical challenges, like having races on broomsticks or wrestling magical creatures in a controlled environment for fitness.
His friends, like Ron and Hermione, are very likely to support him. They've always been there for him in the original story, and in this fanfiction scenario, they would be even more important in his life. Hagrid could also be a great source of support. He has a big heart and has always cared about Harry.
One possible plotline could be Harry taking charge of Hogwarts' security improvements. He might use his unique experiences to set up new magical defenses against the Dark Arts. For example, he could create a network of Patronus guardians around the school, as his own Patronus is very powerful.
Well, he might bring some new strategies. For example, he could use his unique understanding of Voldemort to better protect members. Maybe he would focus more on training the younger members in combat and magic skills, since he knows how important it is to be well - equipped from his own experiences. Also, he might try to reach out to more neutral parties to gain more support against the Dark forces.
In addition to the trio, some fanfictions might focus more on the characters from Slytherin. Draco Malfoy could be a main character in a different light. Instead of being just a rival, he could be an anti - hero or even an ally to Harry. There could also be new original characters created by the fanfiction author that play important roles in the story.
Obviously, Harry Potter is the central character as the title implies. He is the one who is taking control in the story.
His friends from Hogwarts like Hermione and Ron would most likely support him. They have always been by his side through thick and thin in the original story, so in the fanfiction, they would continue to support Harry in his fight against the Ministry.