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.
Ruby could also be a central character in relation to Neo. Their interactions, whether it's a rivalry or an unexpected friendship, can add a lot of depth to the fanfic. Ruby's optimism and leadership skills contrast with Neo's more shadowy personality.
Blake could be another important character. Given her own complex past and her skills, she could have some interesting encounters with Neo. Maybe they have a showdown where they both have to use their acrobatic skills and combat abilities, or they could end up teaming up to take on a greater threat that endangers the Faunus and human relations in Remnant.
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.
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.
One idea could be Neo using her unique abilities in unexpected ways to help the team in a new adventure. Maybe she discovers a new form of her Semblance that gives her an edge in combat.
Typically, Blake and Yang are the key figures. Blake's cool and mysterious nature combined with Yang's fiery personality create an interesting dynamic in these fanfics. Their interactions within the RWBY world, such as during battles or while exploring new areas, are often at the heart of the 'bumblebee futa rwby fanfic'. And the 'bumblebee futa' element adds a unique layer to their relationship and the overall story.
In addition to RWBY, other important characters like Qrow or Ozpin could also be focused on. Qrow has a lot of history and his own future could be intertwined with RWBY's. Ozpin, with his vast knowledge and secrets, might also play a crucial role in how they view the future. His wisdom could be used to help them understand what they see, or he might also be a part of the future they witness in unexpected ways.
One common theme is self - discovery. Neo often has to figure out more about herself in these stories. Another theme is power struggles. Since Neo has her own set of powers, there are often situations where she is in a power struggle with other characters or forces.
Coco Adel could be a really interesting character to focus on in a RWBY Parallel Universe fanfic. Imagine if her love for fashion was not just a hobby but a crucial part of her combat strategy. In the parallel universe, she could design battle outfits that have special abilities. Also, Yatsuhashi Daichi could have a more prominent role. His semblance could be more refined, allowing him to create much larger and more complex barriers that play a vital role in protecting a new, important location in the parallel RWBY world.
One great supporting character could be Velvet. As a Faunus like Blake, she could understand Blake's experiences on a deeper level. They could bond over their shared heritage and Velvet could provide Blake with different perspectives on how to deal with Faunus - related issues. Another option is Qrow. His experience and knowledge of the world of Remnant could be invaluable to Blake. He could act as a mentor figure, guiding her through difficult situations. And finally, Penny. Her unique nature and innocent view of the world could offer a fresh take on things for Blake, and her combat abilities could also come in handy in dangerous situations.
Obviously, Summer and Naruto would be the main focuses. Summer, with her skills and backstory from RWBY, would bring her own set of abilities and relationships to the story. Naruto, on the other hand, is full of energy and has his powerful ninja techniques. Their interactions would be central to the fanfiction.
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.