Ginny would be protective. If there were any fanfictions that she thought were disrespectful to Harry or painted him in a bad light, she'd be angry. But she'd also enjoy the ones that showed the depth of his character and his relationships with others, especially the ones that highlighted his relationship with her.
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.
Others might be a bit shocked at first. But after getting used to it, they could come around. For example, they might initially tease him a little but then realize it's just Harry being Harry and trying something new.
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.
Snape would likely be initially suspicious. He's not used to Harry coming to him for help or sharing secrets. But once he realizes the seriousness of what Harry is saying, he might start to see Harry in a new light. He could be grudgingly helpful, still maintaining his cold exterior but secretly starting to feel a bit more protective of Harry.
Tony would likely laugh at some of the more out - there plot ideas. He'd probably think he could come up with better technology than what's in the fanfic. Steve would be more open - minded and might enjoy the creativity. Thor would be like 'This is not like any Midgardian story I've heard!'.
Some Avengers might be amused. For instance, Tony Stark would likely find it a fun distraction from his usual high - tech world and might even make sarcastic comments about the plot or characters. He could say something like 'These wizards should really upgrade their transportation - brooms? Seriously?'.
Draco Malfoy would probably be outraged at first if he read fanfiction that showed him in a positive light towards Harry and his friends. He's so used to being on the opposite side, but then he might secretly be a bit flattered by some of the more complex characterizations of him.
Some of them would be entertained. Iron Man might laugh at the strange spells and potions. Hulk might not understand much but could enjoy the action parts if there are any. Thor could be curious about the magic and how it compares to his Asgardian powers.
He might be shocked. The fanfiction could have ideas that are completely contrary to his understanding of the future in the wizarding world.
They might be shocked at first. I mean, seeing their own stories being written in a different way by fans would be quite unexpected. Sirius might find it really cool and be eager to read more, while James could be a bit more critical, thinking about how accurate the portrayal is. Remus would probably be more laid - back and just enjoy the different interpretations.