Well, you could have a plot where the OC is a healer - type with a quirk that can cure any injury or illness. However, there's a catch - using the quirk drains the OC's own life force. The BNHA characters initially doubt the OC's abilities because they seem too good to be true. As the story progresses, the OC proves their worth during a major battle where many heroes are injured. They have to decide how much of their own life they are willing to sacrifice to save others, and this creates a deep emotional and moral dilemma.
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.
Maybe in the 'bnha graduation fanfic', there's a competition among the students as part of the graduation. The winner gets a special internship or a chance to work with a top hero. This could lead to intense rivalries and unexpected alliances.
Maybe the Knuckle Duster has a hidden backstory that the OC discovers. The OC could be on a quest to find out more about the origin of the Knuckle Duster, which could involve delving into the history of some secret organization in the BNHA world. Along the way, they form alliances with other characters and face various challenges.
I really like 'Villainous Intent: An OC's Tale'. This fanfic does a great job of integrating the OC villain into the existing BNHA world. It shows how the OC interacts with the well - known heroes and villains from the original story, and the plot twists are really exciting.
One great bnha oc fanfic is 'Rising Star'. It has an amazing original character who is trying to find their place in the U.A. High School environment. The character development is really well - done.
A good plot could be a villain being sent to an alternate dimension where they experience a life without quirks. They see how normal people live and cooperate, and this makes them realize that their use of power for evil was wrong. When they return to their own world, they are determined to reform.
One idea could be focusing on the children of the main BNHA characters dealing with new villains who have unique powers. They could struggle to live up to their parents' legacies while also finding their own identities.
One idea could be a hero with an illusion quirk who uses it to create false distractions during battles. For example, making the villains see an army of heroes when there are really only a few, causing them to waste their attacks and energy.
One idea could be exploring how the characters' relationships change. For example, if Deku was a girl, how would her dynamic with Bakugo be different? Maybe Bakugo would be more protective in a different way. Another plot could focus on how the female versions of the male heroes deal with the challenges in the hero society, like discrimination that might be specific to female heroes. Also, a plot could revolve around a genderbend All Might and how she inspires the new generation of heroes.
Perhaps the OC is a scientist who has been researching a new form of energy. This energy is actually what powers the Sekirei. The OC's research attracts the attention of a group of Sekirei. One Sekirei in particular befriends the OC to learn more about this energy. As they spend time together, the OC begins to understand the Sekirei's world better and helps them find a way to break free from the constraints of the Sekirei Plan.