Maybe the ghosts are the victims of villains. They seek Izuku's help to bring their killers to justice. This could add a whole new layer of moral and emotional complexity to the story. Izuku would have to balance his regular hero duties with this new mission of helping the ghosts find peace.
It could be integrated through a quirk accident. Maybe Izuku is exposed to some strange energy during a battle or an experiment gone wrong, and this gives him the ability to see ghosts. This would be a believable way to introduce the concept within the context of the BNHA world's science - based quirks.
One interesting plot point could be Izuku using his knowledge from the future to change certain events in the past. For example, he might prevent some villains from rising to power earlier. Another could be his interactions with his younger self, guiding and mentoring him in a way that speeds up his growth as a hero. He could also have an impact on the relationships between other characters, like All Might and his predecessors.
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.
In 'bnha izuku detective fanfic', it's interesting because it often explores the underbelly of the hero society. Izuku, as a detective, might uncover things that the heroes don't see. For example, he could be investigating cases related to the illegal use of quirks or the seedy side of quirk trafficking. This gives a different perspective on the BNHA universe and keeps readers hooked as they discover these hidden aspects along with Izuku.
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.
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.
A plot for this fanfic could be that Izuku discovers his sand quirk at a crucial moment during a battle. From then on, he starts to train intensively with it. The story could focus on his growth as a hero with this new quirk. He might have to participate in special training sessions designed for quirks like his. There could be a tournament arc where he shows off his new abilities. However, he also has to deal with the fact that some people are skeptical of his sudden change in quirk, and he has to prove himself not only to his enemies but also to those who doubt him.