One possible plotline could be that Cinder starts off secretly admiring Pyrrha's combat skills. Maybe she spies on Pyrrha's training sessions and tries to learn from her techniques. This could lead to a situation where Cinder has an internal struggle between her admiration for Pyrrha and her own dark motives in the main RWBY storyline.
Perhaps Cinder, as a Pyrrha fan in the fanfiction, could try to befriend Pyrrha. She might approach Pyrrha under a false identity or guise, and as they interact, Pyrrha's positive influence could start to make Cinder question her own evil ways. This would create a lot of tension as Cinder has to balance her new - found respect for Pyrrha with her loyalty to Salem.
One possible fanfiction idea could be that Cinder and Pyrrha are long - lost sisters separated by some dark event in their past. In this fanfic, Cinder could be on a journey of redemption after realizing her sister is Pyrrha. Pyrrha, on the other hand, might struggle with the idea at first but then come to accept Cinder. Their relationship could develop as they face common enemies in the RWBY universe.
In a fanfiction centered around their sisterly bond, Cinder and Pyrrha might have a telepathic connection due to their sisterhood. This could be used in battle situations, like when Pyrrha is in trouble, Cinder senses it and comes to her rescue. Their bond could also be a source of inner strength for both of them, especially in the face of the great challenges in the RWBY world.
It would greatly affect her relationship with Emerald and Mercury. They might be confused as to why Cinder is so interested in Pyrrha. Emerald could feel jealous, thinking that Cinder is replacing her with Pyrrha in some way. Mercury, on the other hand, might just be indifferent or find it strange.
Perhaps in the 'rwby pyrrha returns fanfic', Pyrrha returns with a mission to redeem herself. She could have made some sort of deal during her absence that now requires her to complete certain tasks to save Remnant. This would involve her working with RWBY and other allies, while also dealing with the mixed feelings her friends have about her return.
One possible storyline could be a redemption arc for Cinder through her relationship with Pyrrha. Maybe in an alternate universe, Cinder realizes the error of her ways and Pyrrha helps her to change. They could start as enemies but gradually come to understand each other.
Cinder is often portrayed as complex. Her usual cold and calculating nature might be softened in fanfiction when it comes to her relationship with Pyrrha. She could show vulnerability that she doesn't usually display. Pyrrha, on the other hand, is typically shown as the more empathetic and moral one. She might be the one to reach out to Cinder and try to understand her motives.
A third plotline could involve Cinder being part of a slave rebellion. She could be a reluctant leader at first, but as she sees the injustice and the suffering of her fellow slaves, she becomes more determined. Along the way, she has to deal with the power - hungry slavers and also the complex politics within the slave community. This would be a very action - packed and character - driven plotline, exploring different aspects of Cinder's character and the RWBY world.
Since we should avoid inappropriate content, let's consider the more positive plotlines for Pyrrha in a Yuri - themed RWBY fanfiction. One plotline could be Pyrrha forming a deep emotional bond with another female character during their training at Beacon Academy. They might support each other through difficult times, like facing tough Grimm battles or dealing with academic pressure.
One possible plotline could be that Cinder discovers a pair of garnet pants with some sort of magical property. Maybe the pants give her an extra boost in her combat abilities, and she has to keep it a secret from the other characters while using it to her advantage in battles against RWBY and their allies.
Often, in these fanfictions, Pyrrha comes back and has to deal with the aftermath of her 'death'. She might have to regain the trust of her friends who thought she was gone. There are also plotlines where she returns with new powers or abilities. For instance, she could have gained powers from the place she was 'preserved' in while she was 'dead'. Some stories also explore her relationship with Jaune again, now that she's alive, and how they pick up where they left off or start anew.