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.
Perhaps the fanfic could revolve around Cinder being given the garnet pants as a gift from an unknown source. The pants start to influence her in strange ways, like making her have vivid dreams about her past or future. She then tries to figure out the true nature of the pants and how they are related to her own story and her goals in the RWBY universe.
There are so many RWBY fanfics out there that it's hard to single out ones related to 'Cinder RWBY Garnet Pants' without a more in - depth search. You could start by looking at the RWBY section of popular fanfic websites. Use the search function and type in relevant keywords like 'Cinder', 'Garnet Pants' etc. Maybe you'll come across some interesting reads.
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.
One interesting plotline could be exploring Amber's powers in more depth and how Cinder might be affected or influenced by them. For example, Amber could have a hidden ability that Cinder discovers and tries to use for her own gain.
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.
Well, one possible plotline could be Ruby and Cinder being forced to team up in an unexpected situation. Maybe they have to face a common enemy that is far more powerful than either of them alone.
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 good theme could be her redemption. Many fanfic writers might explore the idea of Cinder turning away from her villainous ways and seeking to make amends for her actions. This could involve her having to face the consequences of her past deeds and trying to find a new path in the RWBY world.
A plotline could involve them having to deal with political or power - related issues. Since they might come from different backgrounds in the original story, their marriage could stir up a lot of trouble in the power dynamics of their world. For example, there could be factions that oppose their union, and they have to fight to stay together.
Since I haven't delved into this specific 'rwby enslaved by cinder fanfic', it's hard to say precisely. However, in fanfics like this, it could be that Cinder uses their weaknesses or secrets against them to enslave the RWBY members. It may also show the different reactions of each RWBY character - Ruby's determination to fight back, Weiss's pride being challenged, Blake's struggle with her past and how it relates to this new situation, and Yang's strength being put to the test in this enslaved context.
Another aspect that makes a RWBY Cinder fanfic good is the way it interacts with the existing RWBY lore. It should respect the established rules and characters of the world while still being able to bring something new. A fanfic that can seamlessly blend Cinder's story with the broader RWBY narrative, whether it's about the huntsmen academies, the Grimm, or the politics of the world, is likely to be a great read. Also, the fanfic should have some sort of emotional impact, whether it's making the reader cheer for Cinder, fear her, or feel sorry for her.