Well, aside from the RWBY team and their associated characters, it's possible that some original Earth characters could become main characters too. For example, a scientist who discovers the Remnant beings and helps them understand Earth technology, or a street - smart kid who shows the RWBY characters the ropes in a big city. These new characters could bring fresh perspectives and new storylines to the fanfiction.
One interesting idea could be how the characters from Remnant adapt to Earth's culture. For example, they might be shocked by the variety of technology or social norms. Another idea could be the new relationships they form with Earthlings. Maybe they team up with humans to fight a common enemy that exists on Earth.
Blake Belladonna is another character that often features prominently in fanfiction. Her complex backstory, especially her past with the White Fang, can be explored in new ways when combined with the concept of Remnant and Earth. Whether she's on Earth learning about different forms of equality or teaching Earthlings about the Faunus on Remnant, she's a great character for fanfiction.
Ruby is likely to be very popular. Her silver - eyed warrior abilities and her positive attitude would make her stand out in any story. Weiss could also be popular, with her Schnee family background and ice - based powers.
Since I haven't read this specific fanfiction, I can't say for sure. But it could be the Remnant knight as the main character, and perhaps some other RWBY - related characters like Ruby, Weiss, Blake, or Yang might make an appearance.
Ruby could definitely be a main character. She has a curious nature and would be very interested in exploring the new American - influenced elements in Remnant. Weiss might also be a main character as she comes from a wealthy and influential family, and she could play a role in how the new American - like concepts are received in the upper echelons of society. Blake could be involved as well, perhaps using her knowledge and experience to analyze how these new ideas might impact the Faunus community. And of course, Yang, with her bold and fearless personality, would be right in the middle of any action or change related to the American influence in Remnant.
There's also a possibility that some of the minor RWBY characters become the main focus in this fanfiction. For instance, characters like Jaune or Pyrrha could be central to the story if the curse has something to do with their past or their abilities. Maybe Jaune discovers that he has a special connection to the curse because of his family's history in Remnant, and he has to take on a bigger role to deal with it, much like how in Dark Souls the player character often has a unique destiny related to the world's curses.
Obviously, Percy would be the main character. Since he is the one sent to Tartarus. Annabeth might also play an important role, even if she's not in Tartarus with him at first. She could be on the surface world trying to figure out a way to get to him or send help. Grover could be another likely character. His connection to nature might come in handy in some way, like if there are strange nature - based elements in Tartarus that only he can understand or control.
Another concept might be the crossover of powers. In some fanfictions, Earthlings could gain the powers of the RWBY characters, like semblances. This would lead to all kinds of new storylines, such as how they would use these powers for good or evil. It could also explore how the RWBY characters would train Earthlings to control these newfound abilities.
Most likely Ruby, Weiss, Blake, and Yang from RWBY will be main characters. Since it's a RWBY crossover, they are the core of the RWBY universe and would be the ones to enter the 'heaven' in the fanfiction.
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'.