Shikamaru would be lazy about it at first. He might think it's a waste of time. But once he starts reading, he'd get drawn in by the interesting plot twists. He'd then start to analyze how the fanfiction changes the existing dynamics between the characters and might come up with his own theories about how the story could continue.
Sakura would be a bit more critical. She would check if the fanfiction portrays her accurately in terms of her strength and her relationships. If it doesn't, she might be tempted to write a comment correcting the author. But if it does, she would be flattered.
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.
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.
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.
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.
There are also those who would be intrigued. Clary, being the curious one, would probably read fanfiction with great interest. She might be amazed at the different ways fans have imagined the story continuing or the relationships evolving. She could even get some inspiration from it for her own adventures, thinking about how the fans' ideas could be incorporated into her real - life challenges in the Shadowhunter world.
For Harry Potter characters, reading fanfiction could be a strange experience. Ginny might be protective of how she and Harry are portrayed in romantic fanfictions. Neville could be surprised by the confidence some fanfictions give him. In RWBY, Blake might be a bit hesitant at first but then get into the more thought - provoking fanfictions. Pyrrha, if she were still alive, would likely be flattered by the positive portrayals in fanfiction. It would open up a whole new world of how they are perceived by their fans for all of these characters.
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.
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.
Some characters might be flattered. For instance, Rem would probably be happy to see positive portrayals of her loyalty to Subaru. Others, like Roswaal, might be intrigued by the different theories and storylines in the fanfic that revolve around him.
Apollo would probably love it. Since he is the god of poetry and creativity, he'd be intrigued by the different interpretations of himself in fanfiction. He might even get some new inspiration for his own creative works from it.