One idea could be a fanfiction where Ruby discovers a new type of Dust with unique powers. This could lead her on an adventure to find out more about its origin and how it can be used to protect Remnant. Another idea is a story that focuses on Ruby's training with a mysterious mentor who teaches her new combat techniques.
A fanfiction could explore Ruby's relationships with her team members in more depth. For example, a story about how she helps Weiss overcome a personal fear during a mission. Or perhaps a tale where Ruby and Blake bond over their shared love for books and stories, leading to a stronger friendship within the team.
One idea could be a story where Neo and Ruby are forced to team up during a special mission in a mysterious new area. They start off distrusting each other but gradually learn to work together as they face various challenges.
One idea could be a story where Ruby and Scarlet team up to face a new, powerful Grimm that has unique abilities. Maybe it can manipulate time, adding an interesting twist to their battles.
In some 'rwby dark ruby fanfiction', there might be the idea of Ruby being corrupted by an ancient evil force. This could lead to her having to fight against her own nature as she is slowly turned into something she hates. It can also show how her friends try to save her from this dark path, which makes for a really engaging story.
One idea could be Ruby adjusting to her new cyborg body and the enhanced abilities it gives her, like super - strength or advanced weaponry integration. Another could be her facing discrimination from some in the RWBY world who fear or mistrust cyborgs.
One plot idea could be Ruby discovering she has werewolf abilities during a mission. She has to learn to control it while still fighting Grimm. Another could be that in a werewolf form, Ruby has enhanced senses that help her track down a powerful and elusive enemy. Or perhaps she forms a pack with some of her friends who also get werewolf-like powers and they have to protect Vale from a new werewolf - Grimm hybrid threat.
One idea could be Ruby discovering she has some cheetah - like abilities. Maybe she's faster than ever and has to learn how to control this new power. It could add an interesting dynamic to her combat style and how she interacts with her team.
One idea could be that Ruby and Coco team up for a special mission in a dangerous, uncharted part of Remnant. They face new Grimm and have to rely on each other's unique skills to survive. Coco's fashion - sense - related weaponry could combine with Ruby's speed and scythe skills in interesting combat sequences.
A really interesting plot would be if Ruby's Reaper form was somehow connected to an ancient prophecy in the RWBY world. Maybe it was foretold that a Reaper - like figure would either save or doom Remnant. This would put Ruby in a very difficult position, with different factions having different views on her and her new form. Also, a plot where Ruby has to team up with some unlikely allies while in her Reaper form to take on a common threat could be cool. These allies could be former villains who see the greater danger that requires Ruby's power.
One idea could be Ruby having to relearn her combat skills while being deaged. It would add an element of struggle and growth as she tries to regain her former abilities. Maybe she forms new friendships with characters she already knew in a different way because of her new, younger perspective.
One idea could be to create a sibling who has a different combat style. For example, while Ruby uses her scythe and speed, the sibling could be more of a strategic fighter, using traps and illusions. Another idea is to explore their relationship dynamic. Maybe the sibling was always in Ruby's shadow and had to struggle to find their own identity. Or perhaps they have a special bond because of a shared trauma from their past.