Toga might be really into it. She loves things that are different and exciting. The unique characters and the fantasy world of Genshin Impact in the fanfiction would appeal to her sense of adventure. She might even start imagining herself as one of the characters in the fanfic, especially if there are any characters with interesting blood - related quirks (even if it's not exactly the same as in MHA).
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.
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.
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.
Some characters might be very intrigued. For example, Albedo, with his scientific mind, would likely analyze the concepts in the fanfiction related to Earth. He'd be interested in how Earth is depicted, its cultures, and technologies. He might even try to find similarities with Teyvat in terms of elemental powers or social structures.
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.
Some characters would be fascinated. For example, Fischl would likely see it as a grand adventure from another realm. She might even incorporate some of the elements from the Honkai Impact fanfiction into her own delusions. Keqing, on the other hand, would probably approach it more analytically. She would try to understand the logic behind the Honkai Impact world and how it differs from Genshin Impact. She might make notes about the different power - leveling systems and how the characters interact in the fanfiction.
Well, the characters in Genshin Impact might be quite surprised at first. They come from different universes. For example, the art styles are different. Genshin Impact has a more fantastical, open - world kind of style, while Honkai Impact has its own unique and often more action - packed feel. If they were to react to the fanfiction, some might be amused, like Paimon. She would probably find the crossovers in the fanfiction really interesting and keep asking questions about the Honkai Impact characters. And Diluc might be a bit more reserved, but still intrigued to see how the two universes are combined in the fanfiction.
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.
Some students could be inspired. Momo might see how Spider - Man creates his own gadgets in the fanfiction. Since she can create objects with her quirk, she could get ideas for new things to create that would be more useful in combat or rescue situations. And the whole experience might make them more open - minded about different types of heroes and hero stories.
Iida would probably be very vocal about any inappropriate or unethical content in the fanfiction. He has a strong sense of justice and propriety, so if there are any elements that go against his values, he would not hold back in expressing his disapproval.
Toga might be interested in the zombies in a different way. Since she has a fascination with blood, she could study the zombies to see how their blood or 'undead' state works. However, other villains might just be in it for themselves. Dabi, for example, might just burn his way through the zombie hordes without much thought for a grand plan. He'd be more focused on his own survival and causing chaos.