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.
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.
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.
Perhaps the travel agent is a bit of a troublemaker. Instead of suggesting normal wizarding travel destinations, they might try to persuade Harry to visit some off - limit or even illegal magical places. They could tell him about a secret portal to a dimension where dark magic is still being practiced freely, which of course, Harry would have to resist.
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.
The characters in Harry Potter might be quite shocked at first. Hermione would probably be very curious about Wonder Woman's world and powers. Ron might be a bit jealous at first but would come around. In the DC side, Wonder Woman's friends like Steve Trevor would be protective at first. But as they see how happy she is with Harry, they would accept him. The wizarding community would have to adjust to having a superhero as part of their world through marriage, and the superheroes would have to accept a wizard into their midst.
In a fanfiction, the students at Hogwarts would be really intrigued by Hawkeye. They've grown up in a world of magic, and Hawkeye would represent a different kind of power. Neville might look up to Hawkeye as someone who uses their own skills to fight, without relying on magic. Ginny would probably be eager to team up with Hawkeye in any battles or adventures, seeing his potential as an ally in the fight against evil.
Harry would be quite surprised at first. He'd be thrown into a world without magic, yet full of strong emotions and drama. He might feel a bit out of place, but as he gets into the story, he'd start to understand the human nature in it. He could admire the courage of the characters, like how they faced the disaster. And he might also be a bit confused by some of the muggle concepts like the class system on the ship.