The reincarnated character is a main character too. Their actions and decisions drive the story. They have to navigate Neo's life and relationships. And then there are likely antagonists. It could be Salem's minions or other villains from the RWBY series who will be in conflict with the reincarnated Neo and the other characters.
Obviously, Neo would be a main focus as the name implies. Her mysterious and devious nature makes her a really interesting character to write about.
Roman Torchwick could be a likely candidate in some fanfics. Since he had a connection with Neo in the original series, he might be brought back in a fanfic to brainwash her for his own ends. Another one could be Salem. She's always looking for ways to gain an edge, and Neo's skills would be useful to her if she could control her.
Well, perhaps the plot involves the reincarnated character trying to change Neo's fate. Since Neo has had a rather tragic story in RWBY, the new character could try to steer her in a different direction. They might also have to face the same enemies Neo did, but with a different perspective due to their reincarnation.
It could be a combination of villains from both universes. For example, Orochimaru from Naruto could team up with Salem from RWBY. Orochimaru is interested in the power of the Grimm and Salem wants to learn about the power of chakra. Their combined evil could be a huge threat to Naruto and Neo, forcing them to use all their skills to defeat this powerful alliance.
She'll probably interact with Ruby, Weiss, Blake, and Yang. After all, they are the main characters at Beacon.
Well, usually the main character is the one who gets reincarnated with the system. They are often an outsider to the RWBY world at first and have to figure things out. Then there are likely to be the main RWBY characters like Ruby, Weiss, Blake, and Yang who will interact with the reincarnated character.
A 'rwby neo brainwashed fanfic' might explore the concept of Neo being brainwashed, which could lead to a lot of interesting character developments. For example, it could change her relationships with other characters in the RWBY universe. Her actions and decisions would no longer be solely based on her own will, but rather on the influence of the brainwashing. This could create a whole new set of storylines and conflicts.
One possible development is that Neo becomes more protective. As she's going to be a mother, she might become more aggressive in defending herself and her unborn baby from any threats in the RWBY world. This could also lead to her making new alliances or breaking old ones depending on who she perceives as a threat or an ally. Another aspect could be her internal struggle with her new identity as a soon - to - be mother, which could change her personality over time.
One common theme is identity. Since Neo has a rather mysterious past, many fanfics explore who she really is. Another is revenge. Given her actions in the RWBY series, some fanfics have her seeking revenge or others seeking revenge on her.
Ruby is often a popular supporting character. Her optimistic and kind nature can play a big role in Neo's redemption. She might be the one to first offer Neo a chance at redemption. Weiss could also be important. Her strong sense of justice could either be a hindrance or a help to Neo, depending on how the story unfolds. Blake is another one. Given her own past of being on the wrong side, she could relate to Neo and help her on her path.