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.
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.
There's a chance he'd be inspired. The stories of the Naruto characters' determination and growth in the fanfiction could stir something in him. He might think about his own journey as a wizard and how he can further develop his skills and character, taking cues from the Naruto characters' tenacity.
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.
The Avengers' reaction would be a mix of caution and curiosity. Hawkeye might keep his arrow aimed at Harry, ready for any sudden moves. Black Widow would be using her skills to read Harry's body language and try to figure out if he's lying. The Hulk might be held back initially, but if Harry made any sudden or 'threatening' moves, things could get really hairy. Overall, they'd all be on high alert until they understood that Harry was not an enemy but a young wizard with his own set of skills and a good heart.
The Weasleys' reactions would be complex. Arthur, with his curious nature, might study the fanfictions to understand how Muggles view their world. Molly would likely be more conservative in her views, not liking any fanfiction that distorts the family values. The younger Weasleys would be more likely to embrace the creativity, with Fred and George looking for ideas to use in their pranks, and Ginny might enjoy seeing herself in different heroic scenarios.
Hermione would be extremely curious. She would immediately start researching it, trying to figure out its mechanics and where it came from. She might even try to find a way to improve it or adapt it to the wizarding world's technology.
The Dursleys' reaction would be complex. Vernon would be enraged and might even try to burn any fanfiction he found. Petunia would be conflicted. Part of her would be disgusted, but a small part might be a bit curious as she has some connection to the wizarding world through Lily. Dudley might be more interested than his parents, especially if the fanfiction had some action or adventure that appealed to his more adventurous side.