Some MHA characters might be flattered. For example, Midoriya would probably be really excited and take it as a sign of how much he's inspired people. He might even look for positive lessons in the fanfiction to improve himself.
Yang would likely have a big reaction. If the fanfiction shows her in a cool fight scene, she'd be all for it and might even show it off to her friends. But if it portrays her in a negative or weak way, she'd be really annoyed.
Tina, as a strong - willed Auror, might initially be skeptical. She'd be worried about the accuracy of the fanfiction in terms of the real wizarding world she knows. But after some thought, she might realize it's just a bit of fun for the fans and start to see the charm in it. She could even start to correct some of the inaccuracies in a friendly way if she ever had the chance to interact with the fanfiction writers.
Some characters might be flattered. If they are depicted as heroes in the fanfiction, it would boost their egos. For instance, Oliver Queen might enjoy reading about himself as an even greater hero than he already is.
Percy would probably find it hilarious. He has a good sense of humor and would likely enjoy the wild and crazy scenarios fans come up with. He might even share the funnier ones with his friends at Camp Half - Blood.
Naruto, being the open - minded and adventurous type, would likely find it fun to read fanfiction about himself. He could be amused by the creative ideas, even if some are a bit far - fetched. He might even take some of the positive ideas and think about applying them in his real adventures. Rias, however, would approach it more skeptically. As a devil princess, she has a reputation to uphold. She would carefully analyze how the fanfiction portrays her, and if it goes against her values or the image she wants to project, she might be a bit offended. But if there are some good aspects, like new ways of handling her devil powers or relationships, she might consider them.
The Flash would likely find it really entertaining. He might enjoy reading about his super - speed being used in all sorts of crazy ways in the fanfiction. And he could also use it as a way to pass the time when he's not out saving the day. He might even start to wonder if some of the ideas in the fanfiction could actually work in real - life superhero situations.
Naruto would be thrilled. He loves attention and the idea that people are writing stories about him would make him feel really special. He might even try to find the authors and befriend them.
Draco would likely be disdainful at first. He has a high opinion of himself and might not like how some fanfictions depict him. Harry might be more curious and open to it, as he's always been more accepting of different ideas.