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.
Well, the heroes would have to adapt their powers. Uraraka could use her Zero Gravity to lift zombies and drop them from a height. Todoroki might freeze groups of zombies with his ice side. However, they'd also face challenges. The chaos of a zombie apocalypse could disrupt their normal teamwork. And they'd have to deal with the moral dilemma of killing what were once humans, which could be a huge psychological burden for the more empathetic heroes.
One idea could be that the heroes have to use their quirks in new and creative ways to fight off the zombies. For example, Bakugo's explosion quirk could be used to blow up large groups of zombies at once. Another idea is that some of the students get bitten and start to turn, creating a moral dilemma for their classmates on whether to save them or put them down. And a third idea could be that the zombie virus is actually a new type of quirk that has gone out of control, so they need to find the source of this 'quirk' to stop the apocalypse.
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.
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.
Deku would probably be very scared at first but then quickly gather his courage and start using his quirk to fight the zombies. He'd also be looking for ways to save as many people as possible. Bakugo would be more aggressive, charging into groups of zombies without hesitation. He might see it as a chance to prove his strength even more. Ochaco would use her zero - gravity quirk to lift zombies and then drop them from a height, trying to take out multiple at once.
Midoriya and Toga. It's an unexpected pairing because Midoriya is the symbol of hope among heroes and Toga is a rather blood - thirsty villain. But if you think about it, Toga's admiration for heroes could be a starting point. Maybe she could be redeemed or at least have a moment of self - reflection through her interactions with Midoriya.
One possible plot could be that a powerful villain manages to release a virus that turns most of the population into mindless, powerful mutants. The remaining heroes, including the students of UA, have to not only fight these mutants but also find a cure. Deku could be leading the group, trying to figure out how to use his new powers in this chaotic situation.
His quirk could be something like 'Limitless Rage - Transformation'. When he gets angry, his body transforms into the Hulk form, growing in size and strength. The angrier he gets, the more powerful he becomes, similar to how it works in the Hulk's original story.
One interesting My Hero Academia zombie fanfiction is 'Heroes in a Dead World'. It shows how the heroes have to use their quirks in a whole new way against zombie hordes. The character development is really engaging as they struggle to survive and protect the remaining civilians.
In some fanfictions, characters' quirks are actually suppressed by the zombie virus. In 'Quirkless in the Zombie Horde', the main character, who originally had a powerful strength - based quirk, has it weakened. This forces them to rely more on their combat skills and strategic thinking rather than just brute force, which adds a new layer of depth to the story.