Hermione would definitely support Harry. She's always been by his side, and she values justice and the proper use of magic and wizarding laws. She would see the wrong in a fanfiction that misrepresents Harry and would use her vast knowledge to help him in the lawsuit.
It could be that the fanfiction used Harry's likeness without permission in a way that was harmful to his image. Maybe it had Harry involved in illegal or immoral activities that he would never do in the original series, so he decides to take legal action against the author of the fanfic.
Dumbledore could be an unexpected ally. He might see this as an opportunity for Harry to stand up for himself and gain some closure on his difficult childhood. Also, some of the Hogwarts professors, like McGonagall, could be on Harry's side. They have always cared for Harry's well - being and would not tolerate the Dursleys' abuse. And there could be some new magical characters introduced specifically to help Harry in his legal battle, like a wizard lawyer who has a soft spot for underdog cases.
Hermione would most likely support Harry. She's always been his loyal friend and would see the injustice of the Daily Prophet's actions. She could help him research laws in the wizarding world (if there are any regarding slander or privacy) and also use her intelligence to find ways to counter the newspaper's claims.
Well, obviously Harry Potter would be a key witness. He was at the center of many of Umbridge's plots. Hermione would also be there, presenting evidence of academic suppression. But don't forget about Ginny Weasley. She was part of Dumbledore's Army and could testify about how Umbridge tried to break up the group. And then there are the Hogwarts professors. McGonagall, for instance, could give her account of how Umbridge disrupted the normal running of the school and undermined the authority of the real Hogwarts staff.
Hermione would surely support Harry. She's always been by his side, and with her intelligence and knowledge of magic and wizarding laws, she'd be a great asset. Ron would also be there, providing his loyalty and his own brand of courage.
Fred and George Weasley are also favorites. Their mischievous nature can be amplified in fanfictions. They could create new and even more spectacular magical pranks specifically aimed at Umbridge, like turning her office into a never - ending maze of trick stairs and hidden rooms filled with various magical creatures that drive her crazy.
They might have to issue a public apology. This is a common consequence when sued for something like false reporting. It would be a way to try and repair some of the damage done to Harry's reputation.
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.
She would probably be outraged. Umbridge is a strict and conservative character in the original series. Fanfiction often contains ideas that deviate from the 'canon' she adheres to, and she might see it as a threat to the 'proper' understanding of the wizarding world she believes in.
This kind of case could have a significant impact. On one hand, it might lead to a decrease in the number of Snape - related fanfictions as writers become more hesitant. On the other hand, it could also encourage the fanfiction community to develop more original characters and stories that are less likely to get them into legal trouble. It might also prompt discussions about the proper use of existing fictional universes within the community.