Well, you could base it on a what - if scenario. What if the liberation of quirks led to a complete restructuring of society? In the fanfic, the heroes and villains might have to form new alliances. You could also make it about a group of students who secretly experiment with quirk liberation, thinking they can use it for good but things start to spiral out of control. This would add a lot of drama and conflict to the story.
One idea could be exploring the backstories of the members of the Liberation Army in more detail. Maybe show how they came to join and their individual motives.
A third idea is to consider a post - war scenario in the 'boku no hero academia' world where the Meta Liberation Army is trying to rebuild. You could explore how they interact with the heroes and society now that the big battles are over. There could be attempts at reconciliation or more underhanded plots to regain power.
One idea could be a fusion between Deku and All Might. Imagine Deku having not just One For All, but also All Might's combat experience and charisma from the start. It would change the dynamic of his battles and his relationships with other characters. Another idea is fusing Todoroki with a water - based hero, which could enhance his ice and water abilities even more and lead to new and creative ways of using his quirk in combat and rescue situations.
One idea could be to have the heroes and villains participate in a Halloween-themed battle royale. The setting could be a spooky, abandoned city filled with Halloween decorations. Another idea is to have a Halloween party at UA High School where students dress up as different heroes or villains from history. They could then have a contest for the best costume.
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 creating a fanfic where a new student with a unique quirk joins U.A. High School. This new character could have a quirk that is both a blessing and a curse, like the ability to control time but at the cost of their own health. Another idea is to write a story about the villains' backstories in more detail. Maybe explore how they became villains and what events led them to oppose the heroes.
A fanfic about Toga falling in love with a civilian. Since she has such an unusual view of the world, it would be fascinating to see how she handles normal relationship emotions. She would have to hide her true nature from the person she loves, and there could be a lot of drama as she tries to balance her two lives - her life as a villain and her newfound love life.
One idea could be a gamer who gets transported into the Boku no Hero Academia world and has to use their gaming skills to survive and become a hero. For example, they might have an in - game inventory system that they can use to access items that help them in battles.
A cool fanfiction concept could be to have a character lose their quirk and then have to find a new way to be a hero. This would show their determination and resourcefulness. Or, you could write about a new villain who has a quirk that specifically targets the heroes' weaknesses, and how the heroes would have to work together to overcome this threat.
One popular idea is an alternate universe where the characters have different quirks. For example, Bakugo could have a healing quirk instead of his explosive one, which would completely change his character arc and relationships. Another idea is a time - travel fanfic, where a character goes back in time to prevent a major disaster in the My Hero Academia world. It could be Deku traveling back to stop All for One from ever rising to power. And then there are the 'what - if' scenarios, like what if Izuku never got One for All? How would his life and the story unfold without this power?