Harry Potter would likely be on high alert immediately. He has experience with fighting Dark Lords, so he would start gathering his old friends and allies. Hermione would be researching like mad, trying to find any weaknesses of this new Dark Lord. Ron would be a bit more hesitant at first but would soon join the fight. The younger generation, like Ginny and Neville's students, would be both scared and determined to prove themselves in the face of this new threat.
He could be shocked. Maybe there are some fanfictions that take a very dark turn or have unexpected pairings that he never thought of. He'd probably need some time to process such strange ideas. And he might also be curious to see how far the creativity of the fans can go. He might even get some new ideas about his own life from reading some of the more imaginative fanfictions.
The Hogwarts professors would have mixed reactions. Some, like McGonagall, might be hesitant to accept new truths that go against the long - held beliefs of the wizarding community. But others, perhaps the more open - minded ones, would be intrigued and willing to explore further. As for the villains, if they learn of certain truths, it could either make them more desperate or cause them to change their ways. For instance, if Draco Malfoy discovers a truth that makes him question his family's loyalty to Voldemort, it could lead to a major shift in his character arc.
Dumbledore would likely see the nanomachines as an interesting new element in the wizarding world. He would be curious about their potential, but also very aware of the possible dangers. He might try to guide Harry in understanding and controlling the nanomachines. The other students would probably be a mix of fear and excitement. Some would be scared that the nanomachines could be used to harm them, while others would be excited to see what new things Harry could do with them.
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.
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.
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.
The headmaster might be a bit surprised at first. He would likely respect Harry's opinion, though. He has always valued Harry's thoughts and feelings. He may start to think about the implications of fanfiction on the wizarding community and how it might affect the students and the overall perception of Hogwarts.
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.