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.
Maybe there's a crossover in the form of a magical tournament. Characters from both series enter, and they have to fight according to the rules of this strange new tournament. It could lead to some really interesting match - ups, like Gray from Fairy Tail against Soul from Soul Eater. Gray's ice magic against Soul's musical weaponry would be a sight to see.
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 Naruto characters are transported to the Soul Eater world. Naruto's determination could be a great asset in the battle against Kishin Eggs. He might use his shadow clones to surround and overpower the enemies. Another plot could involve the weapons from Soul Eater trying to learn Naruto's ninjutsu. For example, Soul could be interested in the Rasengan and try to incorporate it into his fighting style. Also, Maka's strong sense of justice would blend well with the Naruto characters' values, and they could team up to take on powerful foes together.
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.
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.
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.
The character interactions are also very appealing. Imagining Natsu from Fairy Tail teaming up with Maka from Soul Eater is quite fascinating. They have different personalities but similar goals in a way, like protecting their friends and their respective worlds. It's interesting to see how they would communicate and work together.
Another interesting concept is a fusion of Ichigo's Soul Reaper powers with the weapon - meister system in Soul Eater. Ichigo could form a bond with one of the Soul Eater weapons, like Soul Evans. Their combined powers would create a new and powerful form of combat that has never been seen before in either world.
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.
One idea could be that the Fairy Tail guild members are transported to the RWBY world. They could team up with Team RWBY to fight a common enemy like a new type of Grimm that is resistant to normal Huntsmen and Huntresses' attacks but vulnerable to Fairy Tail's magic. For example, Natsu's fire magic could be really effective against ice - based Grimm.