In a 'rwby meets god fanfic', Ruby, Weiss, Blake and Yang are the most likely main characters as they are the focus of the RWBY franchise. But depending on the direction of the fanfic, other characters like Penny or Jaune could also be important. Maybe Penny has some connection to the god due to her robotic nature, or Jaune could be the one who accidentally stumbles upon the god's arrival and then informs the RWBY team. Still, the RWBY girls will probably be the ones with the most significant interactions with the god.
Well, perhaps in the 'rwby meets god fanfic', the god has come to Remnant (the RWBY world) because there is some sort of imbalance or threat that only the RWBY team can help with. So the god decides to guide them, and along the way, the RWBY characters learn about the true nature of their world and their destinies. They might have to make some difficult choices as the god presents them with different paths.
The god brothers themselves are likely to be main characters. Since it's a 'rwby god brothers fanfic', they would play a central role in the story. Also, the main characters from RWBY, like Ruby, Weiss, Blake, and Yang, might also be main characters as they interact with the god brothers.
Blake could also work well as the main character. Given her past and her connection to the White Fang, she has a lot of internal conflict. The God of Darkness could either prey on that conflict or offer her a way to resolve it in a way that is both tempting and dangerous. This would make for an interesting exploration of her character.
Ruby could be a main character. Her speed and scythe - wielding skills would be really interesting to see in the Titanfall universe. She could quickly adapt to piloting a Titan and use her scythe in new and creative ways during battles.
Ruby could be a main character. Given her leadership skills and her connection to the silver - eyed warriors, she might be on a quest to uncover the secrets of the ancient kingdom that could be related to her powers. Weiss could also be a main character as her family has a long history, and she might discover some link between her family's past and the ancient kingdom.
Obviously, Team RWBY could be the main characters. Ruby could be the pilot or the one in charge of the mech's main weaponry. Weiss could handle the mech's ice - based defense systems. Blake could be in charge of stealth operations using the mech's cloaking features if it has any, and Yang could power up the mech's strength - related functions.
Obviously, the members of Team RWBY - Ruby, Weiss, Blake, and Yang - could be the main characters. Their different personalities and fighting styles would make for an interesting exploration of different workout approaches.
Ozpin is a great choice. His long - lived nature means he has a lot of knowledge about the Great War and could be in a position to influence the events, either directly or through his students.
Blake would make a great main character in such a fanfic. Her past experiences and her ability to think on her feet could be very useful when interacting with the Pride Troopers. And perhaps Jiren from the Pride Troopers could be another main character. His incredible power would be a major factor in any battles or challenges they face.
Another possibility for main characters could be Rainbow Dash from MLP and Blastoise from Pokemon. Rainbow Dash is brave and loves adventures, which would be perfect for exploring the new Pokemon world. Blastoise is strong and reliable. They could form a great team, with Rainbow Dash using her speed to scout ahead and Blastoise using its water attacks to protect them from danger.