Well, you could have a story where a high - school is the setting for the start of the zombie apocalypse. A group of students and teachers have to work together to barricade the school and survive. There could be a love story intertwined within this, like two students who find each other during the chaos. Also, an idea could be that the zombies are actually the result of a failed military experiment. A journalist tries to expose the truth while fighting off the zombies and dodging the military who wants to keep it all a secret.
A group of circus performers survive the zombie apocalypse. They use their unique skills like acrobatics to escape from zombies and their tightrope - walking skills to cross dangerous areas. Another idea is a zombie apocalypse that occurs in a space station. The astronauts have to deal with the undead while also trying to find a way back to Earth.
Another idea is to have the last man encounter some sort of mutated creature that he initially fears but then tries to understand. He could try to communicate with it or at least figure out its behavior. This would add an element of mystery and exploration to the fanfiction.
One idea could be Naruto using his shadow clones to distract the zombies while he and his team find a safe place. Maybe he discovers a new jutsu that can control the zombies instead of just defeating them.
One idea could be that the vampires in Twilight are immune to the zombie virus at first. But then they find out that the zombies are evolving and starting to pose a threat to them too. So they have to team up with the werewolves to fight the zombies. This would create an interesting dynamic as they have their own feuds but are forced to cooperate.
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.
You could write about a group of former magical girl antagonists who now have to team up to stop an even greater evil causing the apocalypse. They would have to put aside their differences and learn to work together. It would be interesting to see how their powers, which were once used for evil, are now redirected towards a good cause.
One idea could be that the villains release a powerful virus that turns most of the population into mindless zombies. The heroes have to not only fight the villains but also deal with the zombie horde. Another could be an apocalyptic event that wipes out most of the world's quirks, and the remaining heroes and villains must adapt to this new powerless world.
One idea could be that the gods have lost their powers due to some ancient curse, and it's up to Percy and his friends to find a way to restore them before the apocalypse fully hits. Maybe they have to journey to the very origin of the gods' power.
One idea could be a gamer who uses their in - game survival skills to lead a group in the real - world zombie apocalypse. For example, they know how to scavenge for resources just like in the games they play.