Harry might initially be shocked and confused. He's used to Hogwarts being his safe haven, so when it turns against him, he'll be at a loss. He may try to prove his innocence by finding evidence or confronting those who are spreading lies.
One possible reason could be misinformation spread by the Ministry of Magic. They might have spread false rumors about Harry being a threat, which influenced the Hogwarts community. For example, if the Daily Prophet printed false stories about Harry's supposed dark magic activities, it could turn some students and staff against him.
It enriches the fandom. New ideas from fanfic can inspire more discussions among fans.
Well, in certain fanfic, Harry could react with more caution. He might be constantly doubting the motives of those around him, even his closest friends. Maybe the author is exploring a 'what if' scenario where Harry has had some experiences that made him more paranoid. So instead of jumping into things like he did in the original story, he takes his time to assess every situation.
He could be initially shocked. Harry, who has trusted Ginny deeply, would find it hard to believe at first. He might go through a period of denial, trying to find excuses for Ginny's actions.
He might be extremely angry and confused. After all, parents are supposed to be the ones you can trust the most. He could start to question everything he knew about his family and himself.
Well, if Harry turns into a cat, Hagrid would be quite worried. He might try to take care of Harry in his cat form, giving him treats and a warm place to sleep. The other students would have a mix of reactions. Some might be scared, thinking it's some sort of dark magic at work. But his closer friends like Neville would be determined to help. Neville might even try some of his own plant - based magic to see if it could help Harry turn back. Snape, of course, would probably be skeptical and think Harry got himself into this mess on purpose.
He may be confused at first. Fanfics can be very different from his real experiences. He might wonder why people write such things about him and his world.
Maybe he hates it because it often distorts the real story or characters he knows. Fanfics can take the story in wild directions that don't align with his own experiences.
Well, Harry Potter is a rather humble character. He might initially feel a bit embarrassed to see himself as the center of so many fictional stories created by fans. If the fanfic portrays him as a hero in new adventures, he would probably be honored. However, if it misrepresents his friends or the values he holds dear, he could be a bit indignant. He would likely approach it with an open mind but also with a sense of protectiveness towards his own story and those he loves.
As time goes on, Harry could start to explore what it means to 'please' Sirius. He might recall their past relationship, the things Sirius likes and dislikes, and try to use that knowledge to his advantage. He may also feel a sense of loyalty towards Sirius that, despite the odd circumstances, makes him more accepting of the situation. For example, he might remember Sirius' love for adventure and try to engage in some magical adventures with him in a way that 'pleases' him.