Yang Xiao Long could be a key character. Her brash and powerful fighting style might be pitted against the kind of foes from the Man of Steel universe. And Weiss Schnee, with her family's influence and her own ice - based powers, could also be in the spotlight. She might have to use her skills in a different context, perhaps in a more technology - heavy and super - powered environment like in Man of Steel.
Clark Kent, when he's not being Superman, could be an interesting focus. His normal life and how it intersects with the RWBY characters' lives at Beacon Academy or elsewhere in the RWBY world could be explored. Blake Belladonna is another likely candidate. Her stealth and agility could be valuable assets in a world filled with powerful beings like in Man of Steel, and her own backstory could add depth to the fanfiction.
Cinder Fall could be a likely betrayer. She's already a villain in the original series, and in a fanfiction, she could pretend to be an ally to one of the RWBY members only to betray them at a crucial moment, perhaps leading them into a trap set by Salem.
Ruby is always a great choice. Her journey from a young huntress - in - training to a more experienced leader provides a lot of material for fanfiction. You can explore her growth, her relationships with her team, and how she copes with the increasing challenges.
In addition to Naruto and Sasuke, Kakashi could play a significant role. As Naruto's mentor, he would need to guide Naruto in controlling and using his new body of steel. He might also be concerned about how this power will affect Naruto's growth as a ninja. Sakura could also be there, perhaps using her medical skills to study Naruto's body and understand the nature of this new power.
Well, one interesting idea could be the combination of the RWBY universe's unique character abilities with the epic scale of the Man of Steel story. Maybe characters from RWBY having to face challenges similar to what Superman does in Man of Steel, like dealing with powerful foes that threaten their world. Another idea might be the exploration of how the different Dust types in RWBY could interact with the technology and powers in the Man of Steel world.
Ruby is a likely candidate. She's already a skilled fighter with her scythe, and her eagerness to learn new techniques would make her adapt well to Santoryu. Her speed and agility could be enhanced with the three - sword style.
Ruby is an obvious choice as she has that lead - character feel. Her naivete and determination are traits that can be paralleled to Dorothy. She would be the one to lead the group through the strange world of Oz.
Obviously Naruto would be one of the main characters as the title implies he is being trained. And then, the RWBY characters like Ruby, Weiss, Blake and Yang would also be main characters since they are the ones doing the training.
Well, Naruto for sure. His immortality gives him a unique place in the story. From RWBY, Yang Xiao Long could be a main character. Her brash and confident fighting style would create an interesting dynamic with Naruto. Blake Belladonna, with her mysterious past and cat - like abilities, might also be a central figure. Her more reserved nature compared to Naruto's open - heartedness could lead to some great character development moments. And of course, Ruby and Weiss as mentioned before, would also be important in shaping the story around an immortal Naruto in the RWBY world.
Obviously, Ruby, Weiss, Blake, and Yang would be main characters. They are the core of RWBY. Ruby with her speed and scythe skills would be crucial in any fight. Weiss, with her ice powers, could freeze some of the terrifying enemies from 'The Evil Within'.
Ruby is a likely winner. She has her powerful scythe, great speed, and strong leadership skills. Her ability to quickly analyze a situation in battle gives her an edge. Weiss also has a good chance. With her Glyphs and powerful summoning abilities, she can control the battlefield. Blake is another one. Her speed and shadow - cloning ability make her a tough opponent. And Yang with her super strength and ability to take a hit and then counterattack fiercely could also be a top contender.