One idea could be a 'what if' scenario where the villains and heroes have to team up against an even greater threat from another dimension. It would be fun to see how characters like Bakugo and Dabi interact in this forced alliance.
A fanfiction could focus on the daily lives of the students at UA in a more comical way. For example, showing a cooking competition among the classes where everyone tries to use their quirks in creative ways to cook, but it all goes horribly wrong in a hilarious manner.
Another plot could be about a new student with a really strange and powerful quirk joining UA. This new character could be from a far - off land and have a completely different understanding of heroics, causing all sorts of chaos and also new friendships to form as the other students try to understand them.
An interesting plot could involve an anti - hero who has a hidden agenda that is not entirely evil but also not in line with the traditional hero goals. Maybe they are trying to expose a corrupt part of the hero society from within. They could form alliances with some villains who also have a vendetta against the corrupt elements. This would create a complex web of relationships and moral dilemmas.
One plot idea could be a villain who is secretly a double agent, working for the heroes all along. They infiltrate the villain group and gather information. Another idea is a hero who loses their quirk and has to rely on their wits and combat skills alone, like Batman in the DC universe. And a villain - hero team - up to face a greater threat that neither can handle alone.
One idea could be that during Halloween, the villains use the spooky season as a cover to carry out a major heist. The heroes have to figure out their plan while also dealing with all the Halloween chaos in the city. For example, there could be trick - or - treaters getting in the way and the villains using Halloween decorations to hide their traps.
One idea could be reincarnating as a minor villain and trying to reform. For example, using knowledge of the future to avoid getting caught up in big evil plans. Another could be reincarnating as a quirkless student but finding a unique way to be a hero, like developing amazing combat skills without a quirk. Maybe reincarnating as a side character and becoming the mentor to the main heroes, guiding them with knowledge from the original story.
One idea could be Fumikage exploring a new power within his Dark Shadow. Maybe he discovers a way to temporarily split Dark Shadow into multiple entities, each with a different ability. For example, one could be super fast while another could have enhanced strength.
Another plot could be that the reincarnated person has a unique quirk from their past life that is very different from the quirks in the My Hero Academia universe. This could lead to them being both feared and respected. They might have to go through a lot of training to control it and prove that they are on the side of good.
One idea could be a mystery in the dorms. For example, strange things start happening like items going missing or strange noises at night. The students could team up to solve it, using their different quirks in the process. Another plot could be a friendly competition between the dorm floors, like a quirk - based Olympics. This would show off their abilities and also strengthen the bonds between the students.
One idea could be to explore Overhaul's backstory in more detail. Maybe show how he became so obsessed with 'perfection' and order. For example, you could create a scenario where he had a difficult childhood in a chaotic environment, which led him to strive for the extreme control he desires in the series.
One idea could be an OC with a unique quirk that doesn't seem powerful at first but has a hidden potential. For example, an OC who can manipulate shadows in a very limited way, but discovers they can use it to travel between dimensions in the shadows. Another could be an OC who is a foreign exchange student with a quirk that is considered abnormal in the My Hero Academia world, like a quirk that allows them to communicate with plants and use them as allies in battle. Or an OC who has a quirk that lets them see the future but only in their dreams, and they have to figure out how to use this information to help their classmates and heroes.
One idea could be that the cats have quirks just like the human characters in My Hero Academia. For example, a cat could have a super - speed quirk and be part of a cat - hero team that helps the human heroes in secret. Another plot could involve a cat that can communicate with all other animals and uses this ability to gather intelligence for the heroes. Maybe there's a cat villain who uses its cuteness to deceive people and steal valuable items related to quirks.