Another possible main character could be an alien from Earth itself. This character could be the one to introduce the alien culture and technology to the RWBY world. They could be a sort of guide for the RWBY team, helping them understand the intentions of the other aliens and also teaching them new things that could be useful in their fight against the Grimm and other threats in Remnant.
Ruby Rose could definitely be one of the main characters. Her leadership skills and curiosity would make her interested in these aliens from Earth. She might be the one to initiate contact or try to understand their motives.
Well, it could be about a group of RWBY characters encountering aliens that are from Earth but have some unique abilities or cultures. Maybe these aliens have been hidden on Earth all this time and their presence starts to disrupt the balance in Remnant. The RWBY team then has to figure out how to deal with them, whether it's through negotiation or combat.
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.
An old grandfather who lives in the house could be a main character. He has a lot of stories and wisdom. Maybe he has had some previous encounter with aliens when he was young and now he can help the family deal with the situation in the attic. He could be the one to bridge the gap between the humans and the aliens.
For a 'rwby megatron fanfiction', Ozpin could be a main character. He has a lot of knowledge and could potentially figure out a way to deal with Megatron. The RWBY girls would also be main characters as they are the heroes of their world. Megatron would be the main antagonist, driving the conflict in the story with his desire for power and domination.
Edward and Bella would likely still be main characters. Their relationship could be tested in new ways because of the events related to the Earth's movement. For example, if the Earth's movement causes some natural disasters, Edward would be very protective of Bella during such times.
Blake would be a likely main character. As a Faunus herself, she could play a crucial role in guiding Cardin through his new identity. She could share her own experiences of discrimination and help him understand the importance of the Faunus cause. Maybe they could work together to expose some anti - Faunus groups operating within the school or the city.
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.
The Earth Soldier protagonists themselves can be very popular. Fans like to create unique backstories for them, like they were part of a special military unit on Earth before ending up in the RWBY world. Their different fighting styles and personalities draw readers in.
Yang is also a fan favorite. Her brawler - like fighting style and her strong - willed nature can lead to some great interactions in the 'rwby vs earth' setting. She could get into some interesting battles or rivalries with Earth characters.
Obviously, the members of Delta Squad would be main characters. They'd bring their own personalities and abilities to the story.