A great fanfiction could also involve the villains from BNHA being influenced by the madness in the Soul Eater world. The League of Villains could team up with some of the more sinister forces in Soul Eater and create chaos in both universes. It would be a story full of action and moral dilemmas.
One idea could be to have the characters from BNHA attend the Death Weapon Meister Academy in the Soul Eater universe. They could learn about soul resonance and how to handle weapons in a whole new way. For example, Deku could be paired with a unique weapon and struggle to master the new techniques.
Another interesting crossover would be to combine the quirks from BNHA with the concept of souls in Soul Eater. Maybe a character with a fire - based quirk has to deal with a soul that is resistant to heat when trying to devour it. This would create some really cool and challenging scenarios.
Next, when writing the crossover, focus on how the characters would react to the new environment. If Bakugo were to enter the Soul Eater world, he'd probably be very frustrated at first with all the new rules. You should also make sure to balance the elements from both series. Don't over - emphasize one over the other. For example, give equal importance to the development of BNHA - style quirks and Soul Eater - style soul abilities.
Perhaps in this crossover, the concept of the tailed beasts in Naruto are related to the Kishin in Soul Eater. The tailed beasts are seen as powerful and dangerous entities, much like the Kishin. A group of characters from both universes, including Naruto, Maka, and Soul, come together to find a way to either control or destroy these powerful forces that threaten both their worlds. They would have to learn from each other's strengths and weaknesses to succeed.
Well, a cool concept could be the exchange of powers. Maybe Weiss could learn some of Soul Eater's magic - based combat styles and incorporate them into her Glyphs. And for Soul Eater characters, they could gain some knowledge about Dust from the RWBY world. Also, a plot where the two worlds start to merge slowly due to some mysterious force, forcing the characters to adapt and find a way to separate the worlds again.
Maybe Mifune's code of honor clashes with the more chaotic and rule - bending nature of some of the Soul Eater characters. For example, he might not approve of how Black Star is so eager for glory and fame without following proper protocol. This could lead to interesting character development and story arcs for both sides.
Another plot could involve a character from Soul Eater accidentally getting a Hollow - like power and the characters from Bleach having to help them control it. This would be a great way to explore the different power systems in both universes. Soul Eater characters could learn about the inner world of the Zanpakuto from the Bleach side, and in return, the Bleach characters could gain insights into the complex relationships between meisters and their weapons.
One good crossover idea could be to have the characters from My Hero Academia attend the DWMA (Death Weapon Meister Academy) in the Soul Eater world. Imagine Deku trying to learn how to use a Death Scythe! It would be interesting to see how the different power systems interact. For example, quirks vs. the ability to turn into weapons and the use of soul wavelengths.
Perhaps in this crossover, Asura's power is somehow transferred to one of the weapons in the Soul Eater world. This weapon then becomes an uncontrollable force, and the meister has to find a way to either contain or purge the Asura - like power within it. It could also cause a rift between the meister and their friends as they struggle to deal with this new, dangerous situation.
One idea could be that the Fairy Tail mages are sent to the world of Soul Eater on a mission. They could team up with the students from the DWMA to fight a common enemy, like a powerful dark mage who has somehow made a pact with a Kishin. The Fairy Tail members' magic could interact in unexpected ways with the Soul Eater weapons and Meister abilities. For example, Natsu's fire magic might enhance the power of a fire - based weapon in Soul Eater.
One idea could be that the characters from Fairy Tail and Soul Eater end up in a shared world where they have to team up to defeat a new, powerful dark force. For example, Natsu from Fairy Tail and Maka from Soul Eater could form an unlikely duo, with Natsu's fire power and Maka's scythe - wielding skills combining in unique ways during battles.
Perhaps there could be a plot where the two main characters, Ciel and Maka, swap their partners. So Maka has to deal with Sebastian's sly and demonic ways while trying to achieve her goals in the Black Butler world. And Ciel has to work with Soul, a weapon with his own personality. This would force both characters to adapt to new situations and learn from each other's worlds.