An interesting concept would be an OC who has a quirk that is based on art. For example, they can bring paintings to life. This OC could be a part of an art school within the My Hero Academia universe and use their quirk to fight villains who are attacking art galleries or museums. They would also have to train their quirk to be more combat - effective.
An interesting concept for a 'boku no hero academia oc fanfic' is an OC who is a villain at first but then slowly realizes the error of their ways. Their quirk could be something that is initially seen as very menacing, like the power to steal the quirks of others temporarily. As the story progresses, they could start using this quirk for good, like helping heroes regain their lost quirks in battles against stronger villains.
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 Pokemon have quirks like in My Hero Academia. For example, a Pikachu with an electricity - based quirk that allows it to not only use electric attacks but also manipulate the electricity in unique ways, like creating shields. Another idea is to have the characters from My Hero Academia become Pokemon trainers. Deku could start his journey with a weak - looking Pokemon that he trains to become very powerful, just like he does with his quirk. And a third idea could be to set the Pokemon world in the My Hero Academia universe, where there are both heroes and villains trying to control powerful Pokemon for different purposes.
One idea could be to explore the backstory of a minor character. For example, what was the life of a random student in Class 1 - B like before coming to U.A. High? Another could be a 'what if' scenario, like what if Izuku Midoriya didn't get One For All. Maybe he'd develop his own unique quirk through sheer determination and hard work. Or a fanfic could focus on the villains' side, showing how they came to be and their motives in more depth.
One idea could be a crossover with the Harry Potter universe. Imagine Deku going to Hogwarts and learning magic while also using his Quirk. He could make friends with Harry and they could learn from each other's skills. Another idea is a crossover with the Avengers. The heroes from My Hero Academia could team up with the Avengers to fight a common, super - powerful enemy. Maybe All Might and Captain America could have an interesting conversation about leadership and heroism.
One idea could be that the OC's voice quirk is a secret weapon against a new type of villain who can't be defeated by normal quirks. The OC has to keep their quirk hidden until the right moment. Another plot could involve the OC's voice quirk being stolen by a villain, and they have to find a way to get it back. Maybe the OC uses their voice to communicate with animals in the My Hero Academia world, and this leads to an adventure where they have to stop a group of villains who are using animals for evil purposes.
The OC could have a quirk that gives them the ability to see all possible futures. This would make their decision - making in battles very crucial. They might struggle with the weight of this knowledge at first, but as they learn to trust their instincts and use their quirk effectively, they become an invaluable asset to their hero team. They could also use this quirk to prevent major disasters in the My Hero Academia world.
Perhaps the OC has a hidden past related to a villain organization, and the harem members are initially suspicious but as they get to know the OC better, they realize there's more to the story. This could create a lot of drama and conflict as the OC tries to prove their loyalty while also dealing with their growing feelings for the harem members.
One plot idea could be that the OC criminal is secretly working with a high - ranking hero to bring down a powerful villain organization from the inside. Another is that the OC criminal has a personal vendetta against a specific hero and is constantly trying to undermine them. A third idea is that the OC criminal discovers a powerful but dangerous quirk - enhancing drug and is trying to distribute it among the criminal underworld.
Well, you could do a fanfic where the Akatsuki members from Naruto are villains in the My Hero Academia setting. They could be after the quirks of the students. And maybe Deku somehow gets involved with Naruto and they figure out a way to stop the Akatsuki together. Or perhaps a story where All Might meets the Hokage. They could exchange ideas on leadership and heroism.