One idea could be to have characters from Boku no Hero Academia (bnha) and Demon Slayer (kny) participate in a joint training session. For example, Deku from bnha could learn some swordsmanship techniques from Tanjiro of kny. This would create an interesting dynamic as they come from different worlds with different power systems.
Another idea is a crossover where the villains from both universes team up. All For One from bnha and Muzan from kny could form an alliance. This would force the heroes from both series to work together. The heroes would have to figure out how to combine their quirks and breathing techniques to defeat this powerful evil force.
Perhaps there could be a plot where a villain in the bnha world discovers a way to summon demons from the kny world. This causes chaos as the demons start attacking the cities. The heroes and the Demon Slayer Corps then have to team up. The bnha characters use their quirks to support the kny characters in battles, like Bakugo using his explosions to create distractions while the kny characters go in for the kill.
A great one is 'When Demons Meet Heroes'. This fanfic explores how the characters from 'kny' would fare in the world of 'bnha' and vice versa. It has some really cool fight scenes where the skills and quirks from both sides are pitted against each other. It also delves into how the two different cultures in the shows would interact.
Another way is to check out fanfic communities on Reddit. There are subreddits dedicated to both 'Demon Slayer' and 'My Hero Academia' where people might share or recommend 'kny x bnha' fanfics. You can also post a request for such fanfics there and the community might be able to help.
First, understand the core elements of both universes. For bnha, it's the quirks and the hero society, while for kny it's the breathing techniques and the demon slaying corps. Then, find a common ground. Maybe a new type of threat that affects both worlds, like a group of villains who can use both quirks and demon - like powers. This can bring the characters together in a believable way.
Tanjiro and Deku would be a great pairing. Tanjiro's strong sense of justice and determination to protect his loved ones is similar to Deku's. They could learn a lot from each other, with Deku showing Tanjiro about quirks and Tanjiro teaching Deku about breathing techniques. Another interesting pairing could be Bakugo and Inosuke. They both have a fiery temper and are very competitive. Their interactions would be full of energy and probably a lot of arguing at first.
Another interesting concept is a chatroom that exists secretly among the villains. They plot their next moves, argue about the best ways to take on the heroes, and maybe even have some internal power struggles. It would be exciting to see their different personalities clash in this virtual space.
One idea could be a crossover with Harry Potter. Imagine Deku attending Hogwarts and learning magic while also trying to control his One For All quirk. He could make friends with Harry and they could share their experiences of being the 'chosen ones'.
Well, you could start with the costumes. In a genderbend fanfic, the female versions of male heroes might have more stylish or practical costumes. For instance, All Might as a woman could have a more form - fitting suit that still represents her power. You could also play with the backstories. Maybe the female - genderbent Deku had to face different kinds of discrimination in a male - dominated hero world. And of course, there could be new romances or different interpretations of existing friendships.
One idea could be a fanfic where Nezu takes on a mentorship role for a young and struggling hero student. He could use his intelligence and experience to guide the student through difficult challenges.
One idea could be exploring their training days before they became so well - known. Maybe focus on how they overcame their individual weaknesses. For example, Mirio could be shown struggling with a new type of quirk - based obstacle and how he found a creative way to get past it.