A cool fanfiction idea could be Tomura getting transported to another universe where there are no quirks. He'd have to adapt to a completely different world without his powers. It would show his character in a new light as he has to rely on his wits and other skills. This could also lead to him having a different perspective on life and his actions in his own world.
One idea could be exploring Tomura's backstory in more detail. Maybe show his life before he became a villain, his family situation, and what led him to the path of destruction. Another could be a 'what if' scenario, like what if Tomura was redeemed and joined the heroes. He could use his knowledge of the villains to help the heroes take down other threats.
One idea could be exploring Tomura's past in more detail. Maybe show his childhood before he became a villain, how he was influenced by All For One. Another could be a story where Tomura tries to redeem himself, which would be a huge twist from his normal villain role.
It could completely change the dynamics of the story. Maybe Deku would have a different perspective on villains and their motives.
A cool concept for My Hero Academia fanfiction is to have a time - travel plot. A character could go back in time and change a significant event in the My Hero Academia world. This could lead to a completely different storyline. Or you could write a story centered around a villain redemption arc. For instance, giving a more in - depth look at how a villain like Shigaraki could potentially be redeemed and how the heroes would react to that. Additionally, fanfiction about a tournament between different hero agencies could be really exciting.
Dabi could be a great character to pair with Tomura. They are both villains and their powers and personalities could create some interesting interactions. Maybe they could team up for a particularly difficult mission or have a power struggle within the League of Villains.
Give Tomura a new power or ability that is unique to your fanfiction. This will set your story apart from others. For example, he could have the ability to control time for a short period.
One idea could be a story where Eraserhead and Ms. Joke team up on a particularly difficult mission. Maybe they have to infiltrate a villain's lair and their different quirks work in harmony to overcome various obstacles.
One idea could be a story where a character's quirk goes horribly wrong in a very creepy way. For example, if Deku's One For All started to consume his mind instead of empower him, making him lose his sense of self and become a menacing figure. Another could be about a hidden villain within UA who uses their quirk to create disturbing illusions that drive students mad. And a third idea might be a fanfiction where the Nomu are given a more sinister backstory, like they were once normal people whose quirks were brutally experimented on, turning them into the terrifying creatures they are now.
One idea could be exploring the backstories of minor characters during a certain period. For example, how a sidekick trained under a pro - hero before the main events of the series. Another could be a story set during a time when the hero society was in a state of transition, like when new laws about hero work were being introduced.
One idea could be a crossover where Naruto characters end up in the My Hero Academia world. For example, Naruto could meet Midoriya and they could learn from each other's determination. Another could be a story where the quirks in My Hero Academia are similar to the ninja abilities in Naruto. Maybe a character has a quirk like shadow clones. A third idea might be a time - travel fanfiction where a My Hero Academia character goes back in time to the Naruto era and has to adapt to the different fighting styles and cultures there.
One idea could be to have the characters in a medieval setting with their quirks being seen as magic. For example, Deku could be a young squire with a hidden 'power of magic' (his quirk) that he has to keep secret at first. Another idea is to make the League of Villains as a group of outlaws or dark wizards. They could be causing chaos in the medieval kingdom, and the heroes would have to band together as knights or mages to stop them.