Well, Ciel Phantomhive and Shu from Diabolik Lovers might form an alliance in a strange way. Ciel is always looking for ways to gain an edge in his battles and investigations, and Shu, despite his lazy appearance, has his own hidden strengths. Shu might be interested in Ciel's resources and power, while Ciel could see Shu as an unpredictable but potentially valuable asset. Maybe they form an alliance out of mutual need and a bit of curiosity about each other's worlds.
Ayato from Diabolik Lovers and Grell from Black Butler could potentially form an alliance. Ayato is impulsive and full of energy, and Grell is rather wild and has his own unique view of the world. They might team up just for the fun of it or because they both see an opportunity to cause some chaos. Grell could be intrigued by Ayato's vampire nature, and Ayato might find Grell's flamboyance and scythe - wielding skills interesting.
Ruby would be a likely candidate. She is the leader of Team RWBY and has an open - minded nature. She would be able to see beyond Godzilla's initial appearance as a threat and might try to communicate with it. Yang, with her fearless attitude, could also be part of the alliance. She is not afraid to face powerful opponents and would be willing to fight alongside Godzilla if it means protecting the world. Blake, given her experience with different species and her ability to empathize, could also be part of the group that tries to form an alliance with Godzilla.
Batman and Kakashi would be likely to form an alliance. They are both very intelligent and strategic. Batman is known for his detective skills and Kakashi is a highly skilled ninja. They could work together to figure out the motives of the villains in the crossover and come up with a plan to stop them. They would also respect each other's combat abilities.
Sasuke and Duncan might form an alliance. They both have a bit of an edgy and brooding personality. They could respect each other's skills. Sasuke's ninja skills in combat and Duncan's street - smart and tough - guy attitude would make them a formidable pair in any challenges they face in the crossover.
I think Harry Potter and Captain America would be likely to form an alliance. Harry is a natural leader who has faced great evil in his world, and Captain America is all about justice and doing what's right. They would respect each other's values and leadership skills. They could lead their respective teams, the Hogwarts students and the Avengers, in the fight against the common enemies like Voldemort and Thanos.
One idea could be that the characters from Diabolik Lovers end up in the Black Butler universe and are mistaken for demons by the characters there. They then have to deal with Sebastian and Ciel while trying to find a way back to their own world. Another plot could involve a character from Black Butler getting trapped in the Diabolik Lovers' world and having to navigate the complex relationships among the vampire boys.
Natsu from Fairy Tail and Maka from Soul Eater. Natsu is a hot - headed and powerful mage, always eager for a fight. Maka, on the other hand, is a determined Meister with a strong sense of justice. Their common goal of defeating powerful enemies would likely bring them together. Natsu's brute strength and Maka's strategic thinking could make for a great combination in battles.
Percy and Carter would be likely to form an alliance. Percy is used to leading and being in dangerous situations, and Carter has a similar sense of responsibility. They both have powers related to water in a way (Percy's direct control of water and Carter's connection to the Nile). Their leadership skills would make them work well together to face any common threats in the crossover world.
Ruby and Church could form an alliance. Ruby is always eager to make new friends and fight for what's right. Church, despite his snarky attitude, has a good heart deep down. They could bond over their leadership roles in their respective teams and share their knowledge about combat and strategy.
I think Yugi and Captain America would be likely to form an alliance first. Yugi is a kind - hearted and brave character, and Captain America is all about justice and leadership. They would recognize these qualities in each other quickly and start to work together to face the challenges in the crossover situation.
Probably Henry and Babe. Henry is used to taking charge and being a leader in his world of fighting crime. Babe is the creative and business - minded leader of the Game Shakers. They both have strong personalities and leadership qualities. So, when they first meet in a crossover situation, they would likely recognize those qualities in each other and form an alliance quickly to deal with whatever problem has brought their two worlds together.