How about a story where a group of villains and heroes are transported to an alternate dimension where the roles are reversed? The heroes now have to survive in a world that hunts them, and the villains find themselves in a position of power where they have to decide whether to be good or continue their evil ways. Another plot could be a villain who creates a quirk - enhancing drug that starts to spread among the heroes, causing chaos as some heroes become addicted and lose control of their enhanced powers.
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 the 'Villain Class 1A' has to team up with the real Class 1A to fight a greater threat. Maybe a new super - villain emerges who is too powerful for either group alone. This would lead to some really interesting character dynamics as they have to put aside their differences.
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.
Another plot could involve Ochako being manipulated by a charismatic villain. This villain convinces her that the hero society is corrupt and that by joining the 'dark side' she can actually make a more positive change. She then uses her gravity quirk to disrupt hero operations, like making heroes' equipment float away during battles.
One plot idea could be that your OC is wrongly accused of being a villain because their methods of killing villains are too extreme for the hero society. They then have to prove their innocence while still continuing to hunt down the real villains. Another idea is that a powerful villain organization puts a bounty on your OC's head, and they have to fight off assassins while also taking on the main villains.
One idea could be creating a new hero with a unique quirk that challenges the existing power dynamics in the My Hero Academia world. For example, a quirk that can nullify other quirks temporarily.
One plot idea could be exploring Magne's backstory in more depth. Maybe she has a hidden family or a past encounter that shaped her into the character she is in the series. Another idea is a what - if scenario where Magne teams up with unexpected heroes or villains from the My Hero Academia universe.
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 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 that the main character has a gamer ability that allows them to level up their hero skills like in a game. For example, they earn experience points for every good deed or fight they win. Another plot could involve a gamer from our world getting transported into the My Hero Academia universe and using their gaming knowledge to outwit villains. Maybe they introduce new 'game mechanics' to the hero world, like quests for heroes to complete for special rewards.
Another plot could involve Backdraft teaming up with some of the students from U.A. High. He could teach them some advanced fire - fighting and rescue techniques specific to his quirk.