I think Jack Frost from 'Rise of the Guardians' and Robin from 'Young Justice' would be likely to form an alliance first. Jack is always looking for adventure and a chance to prove himself, and Robin is very strategic and open - minded. They would probably recognize each other's skills quickly and decide to work together.
Another possibility is Tooth from 'Rise of the Guardians' and Artemis from 'Young Justice'. Tooth is very caring and focused on protecting something precious (teeth, in her case, which are like a form of life essence). Artemis is also very protective and has a sharp eye. They might bond over their protective natures and form an alliance to keep an eye on the more impulsive members of their respective groups.
Superboy from Young Justice might also be a likely candidate. He's often looking for his place and trying to prove himself. Meeting the Bat family could be a chance for him to show what he can do. He might be a bit brash at first, but once he realizes they are all on the same side, he could be quick to form an alliance. He could see Batman as a role model in a way, someone who is strong and has a sense of justice.
Probably Naruto and Iron Man. Iron Man is always interested in new technology and abilities. When he sees Naruto's unique ninja abilities, especially the jutsu like Rasengan which is like a concentrated energy attack, he would be intrigued. Naruto, on the other hand, would be interested in Iron Man's high - tech gadgets. So they would start an alliance based on mutual curiosity and the potential of combining their skills.
Spiderman himself could be the one to initiate an alliance. He's used to working with other heroes and he has a friendly personality. When he meets the Batfam, he would see the potential in working together and might reach out first. He would probably start with some light - hearted banter to break the ice and then suggest they team up to take on the bad guys in Gotham.
It could also be Annabeth and Black Widow. Both are highly intelligent and strategic. Annabeth's knowledge of architecture and ancient languages might be useful to Black Widow in certain situations, like deciphering an ancient code related to a new threat. Black Widow, in turn, could teach Annabeth some self - defense and espionage skills. They would see the value in each other's abilities and form an alliance quickly.
Another possibility is that Tony Stark and Nami would be the first to start an alliance. Nami is always interested in valuable things, and Tony has a lot of high - tech gadgets. They could start a business - like relationship at first, with Nami being intrigued by Stark's technology and Stark being impressed by Nami's navigation skills and her ability to handle money. This could then lead to a full - fledged alliance between the two groups.
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.
I think Hamilton and Captain America would be likely to form an alliance. They both have strong beliefs in justice and freedom. Captain America fought for his country in a different time, and Hamilton was a key figure in the American Revolution. They could understand each other's values and work together towards some common goals, whether it's about protecting the people or promoting certain ideals.
Sasuke and Stealth Elf. Sasuke is a skilled and somewhat brooding character, and Stealth Elf's stealth abilities would complement Sasuke's own combat skills well. They could work together in a more stealth - based mission in a fanfiction, like infiltrating an enemy base.
Leonardo and Piccolo could form an alliance. Leonardo is a natural leader and very disciplined, which Piccolo can respect. Piccolo, with his strategic mind and powerful abilities, would be a great ally for Leonardo in battles. They could work together to plan attacks against their enemies, like when facing a powerful villain that has both ninja - like stealth and superhuman strength.
Probably Naruto and Robin. Robin is the leader - type in Young Justice, always thinking and strategizing. When Naruto shows up, Robin would be the one to approach him first, trying to figure out who he is and what his intentions are. Naruto, being friendly and curious, would be open to the interaction.