One common theme could be power and ambition. Cinder is a very ambitious character in RWBY, and in fanfics, this could be explored further, especially in relation to her 'futa' aspect which might be used to emphasize her dominance. Another theme might be redemption. Some fanfics could explore the idea of Cinder finding a path to redemption despite her actions in the original series.
Well, often there is a theme of conflict. Given Cinder's complex character, there could be internal conflict within her, especially if the 'futa' aspect adds another layer to her identity. This could be in conflict with other characters in the RWBY universe. Also, themes of love and relationships might be present. Cinder's relationships, be it romantic or platonic, could be re - imagined in these fanfics, and the 'futa' element might play a role in how she interacts with others.
A common theme in RWBY Cinder Futa fanfic could be transformation. The 'futa' concept might be used as a form of transformation for Cinder, either physically or in terms of her character development. This transformation could then lead to new storylines, such as her taking on new roles or facing different challenges. Additionally, themes of secrecy and revelation might be present, as Cinder might hide or reveal her 'futa' side depending on the plot of the fanfic.