Harry might be initially shocked and angry. He has always considered England his home and fought for it. So, being kicked out would be a huge blow. He may try to fight back, using his magic to resist the unjust decision. However, if he realizes that resistance is futile, he could leave with a sense of bitterness and a determination to one day clear his name.
Harry may react with a sense of defiance. He has faced many challenges before, and being kicked out won't stop him. He might immediately start planning to expose the truth behind his expulsion. He could reach out to his closest friends, like Hermione and Ron, and together they could form a plan to uncover the conspiracy. He may also feel a sense of betrayal from the wizarding world he has always protected.
One possible reason could be that in the fanfiction, the wizarding community in England has turned against Harry due to some false accusations. Maybe a powerful dark wizard has framed him for a series of heinous crimes, and the public, being misled, forces him to leave. Another reason might be political intrigue within the Ministry of Magic. There could be a new regime that sees Harry as a threat to their power and thus kicks him out.
Yes, there are quite a few. Some might stand out for their unique take on combining the magical world of Harry Potter with a fictional take on a 'Prince of England' in the fanfiction realm. For example, those that create interesting relationships between the Potter characters and this royal - like perhaps a plot where the Prince has to deal with a wizarding threat and enlists Harry's help.
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.
He might be very sad at first. Harry has always valued his friends, so being forgotten by them would be a huge blow.
At first, Harry would probably be in shock. He has always considered Hermione one of his closest friends, so her betrayal would be a huge blow. He might not believe it at first and try to reason with her.
Harry might react with shock. If he overhears something unexpected like Ron and Hermione confessing their love for each other, it would be a big surprise. He might stand there frozen for a moment, not knowing how to process it.
Harry would likely be defiant at first. He has a strong sense of justice and would not easily submit to Voldemort's punishments. For example, if Voldemort uses the Cruciatus Curse, Harry would probably try to resist the pain and not show weakness.
He might be shocked at first. Discovering that he isn't a Potter is like shattering his whole identity. He could feel lost and confused, not knowing who he really is anymore.
Harry could also be angry. Despite understanding Dumbledore's generally good intentions, being tied to a bed against his will is a violation of his freedom. He might struggle against the restraints and demand to be released immediately, especially if he feels that Dumbledore is overstepping his boundaries.
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.