I think Weiss could also be a strong contender. She comes from a powerful family and has been training in combat and her glyph abilities for a long time. In fanfiction, she could discover a way to unlock the super saiyan form through her study of ancient magic or family secrets. Once she achieves it, she could use her intelligence and strategic thinking to make the most of the new power, while also looking really cool with super saiyan - like hair.
Yang might be the one. She has a very strong will and her semblance is related to her strength and rage. Super Saiyan transformation is often associated with a burst of power and emotion, which Yang already has in abundance. When she gets really angry, she could potentially tap into the super saiyan power. And her combat - oriented personality would make her a great candidate to show off the new form in battles.
Ruby could be a likely candidate. She has that natural leadership quality and a strong drive to protect others. Her silver - eyed power already shows she has some latent and unique abilities. Combining that with the super saiyan form could make her an even more formidable fighter. Also, she's the main character, so it would be a great plot twist to see her achieve this form first.
I think Naruto and Ruby would be likely to form an alliance. Naruto is always eager to make friends and help others, and Ruby has a similar kind of positive, can - do attitude. They both lead their respective teams in their own universes, so they would understand each other's leadership roles and could work well together.
Ruby. She has a very open - minded and empathetic nature. She would likely be the first to try and reach out to the Arkham Knight, believing that there is good in everyone. She might see his skills and think that, if redirected, he could be a great asset in fighting the Grimm.
Black Widow could be the first to form a friendship with Elsa. Black Widow is very perceptive, and she would quickly realize that Elsa is not a threat but a potential ally. She has a way of getting close to people and making them feel comfortable. She could help Elsa adjust to the new and strange world of the Avengers, and they could bond over their shared experiences of being different from the rest of the group. Elsa's powers would also be something that Black Widow could see as a valuable asset in their missions.
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.
Ruby's character would likely become more confident. The Super Saiyan power is extremely powerful, and having it would make her realize she can take on much greater threats. For example, she might be more willing to take the lead in battles against the Grimm.
Cindy and Penny might form a strong bond. Cindy is a mechanic in FFXV, and Penny is a robotic girl in RWBY. Cindy could be interested in Penny's mechanics and construction, and Penny could learn from Cindy's more traditional engineering skills. They could work together to upgrade or repair machinery in the crossover setting.
Ruby. She's extremely fast and has shown great combat skills. Her ability to quickly move in and out of danger would give her an edge against a Xenomorph. Also, she has a strong sense of determination which would help her stay focused during such a terrifying encounter.
Zero and Ruby would be a likely pairing. Zero is a powerful and skilled fighter, and Ruby has a lot of potential and a unique weapon. They could learn from each other's combat styles. Ruby could learn about Zero's more serious and battle - hardened approach, while Zero could be inspired by Ruby's enthusiasm and creativity in fighting.
I think Ruby and a young, adventurous Pilot would make a great pairing. Ruby's enthusiasm and eagerness to learn new things would mesh well with a Pilot's daredevil nature. They could exchange stories about their respective worlds while fighting side by side.
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.