Some of them might be excited to see new stories in a different superhero universe. For instance, Ruby might be really into it, seeing the unique quirks as something cool and inspiring.
They might be really surprised. Some characters could be flattered by the positive portrayals in the fanfiction, while others might be a bit annoyed if their personalities are misrepresented. For example, Deku might be shy but also happy to see new interpretations of his growth journey.
Shigaraki would likely be disgusted if the fanfic made him seem weak or less of a threat. He'd probably scratch at his neck in irritation. Dabi would be dismissive. He'd think fanfics are just a waste of time and not worthy of his attention. Toga, though, might be intrigued. If the fanfic had a lot of blood and gore in it, or if it focused on her relationships in an interesting way, she could be really into it.
They may be either amused or annoyed. It depends on how they are portrayed in the fanfiction. If it's a positive and creative portrayal, they might be amused. But if it's a negative or inaccurate one, they could be annoyed.
Shigaraki would likely be dismissive. He's so focused on his own goals of destroying the hero society that he'd see fanfiction as a useless distraction. However, if there were elements in the Genshin Impact fanfic that could somehow be related to his own plans, like powerful artifacts or magic that could be used for destruction, he might take a second look.
Another scenario could be the characters reacting to different versions of themselves from alternate universes. They might be shocked to see how different they could be in terms of personality or appearance. For instance, Midoriya seeing a version of himself who is a villain. This would lead to a lot of self - reflection and internal conflict among the characters.
Some characters might be intrigued. For example, Izuku Midoriya would probably be very interested in understanding how the Gamer Sparda powers work. He would see it as a new type of quirk to study and might try to find ways to incorporate the strategies used in the 'game' aspect into his own hero training.
The students of Class 1 - A would have a range of reactions. Ochaco might find the romantic elements in the fanfiction really sweet, especially if there are any cute ship moments. Iida would likely be concerned about whether the fanfiction adheres to some sort of moral code. He might be nitpicky about things like fairness and justice within the fictional story.
The characters would have a range of reactions. Some would be in disbelief. They have witnessed Deku's journey from a quirkless boy to a powerful hero - in - training. So, seeing him as a villain in a fanfiction would be like a complete 180 - degree turn. Midoriya's mother would be devastated. She has always supported her son, and to see him as a villain would go against everything she believed in. The teachers at U.A. would be concerned and start to analyze what could have led to this change. Maybe they would question their own teaching methods or if there were any signs they missed during Deku's time at the school.