Well, a cool fanfiction concept could be a fusion of their powers. Maybe Cinder's ability to control fire and Naruto's Rasengan could combine into a super - powerful attack. Also, Naruto could introduce the concept of friendship and loyalty to Cinder, which she may not be very familiar with in her original world, and this could change her character development. And what if Naruto's shadow clones are used in a strategic way to deceive Cinder's enemies?
To make it unique, you could give Cinder some of Naruto's ninja abilities like the ability to walk on walls or use substitution jutsu. This would be a really unexpected twist for readers who know Cinder from her original story.
In lemon fanfiction, Cinder Fall might often be portrayed as more seductive. Her usual confident and powerful traits in the original RWBY series can be enhanced and sometimes used in a more alluring way to drive the romantic or more adult - themed aspects of the story.
Power is a common theme. Cinder is often depicted as either seeking more power or dealing with the consequences of her power - hungry actions. Another theme is redemption. Some fanfictions explore if she can be redeemed after all the bad things she's done.
One common theme could be the clash of two different worlds. Naruto comes from a ninja - filled world, while Cinder Fall is from a world with its own set of powers and politics. So, exploring how they adapt to each other's worlds is often seen. For example, Naruto might be amazed by the technology in Cinder's world, and Cinder could be intrigued by Naruto's chakra abilities.
Perhaps in a crossover fanfiction, there's a magical grocery store that exists between their two worlds. Naruto and Cinder both end up there by accident. Naruto is excited to try new things and Cinder is more cautious. They could form an unlikely alliance as they deal with the strange storekeeper who has his own motives for bringing them together.
One idea could be a crossover where Cinder somehow gets transported to the Naruto universe. She might initially try to use her powers to gain control, but then realizes she has to adapt to the new chakra - based powers. Meanwhile, RWBY characters could also end up in the Naruto world in search of Cinder and end up forming unexpected alliances with Naruto and his friends.
Well, one popular place to find Cinder Fall fanfiction is Archive of Our Own (AO3). Just search for 'Cinder Fall' and then look through the results to find the ones that might be considered 'lemon' if that's what you're into. But be aware that some fanfictions might have mature content.
I really like 'Cinder Fall: The Hidden Power'. In this fanfiction, Cinder discovers a new and unexpected power within herself. The author does a great job of integrating this new element into the existing RWBY universe. It also has some interesting interactions between Cinder and other characters, like Ruby and Weiss, which adds more depth to the story.
Love against all odds is also a big theme. Given Cinder's nature and the world she exists in, the relationship between her and the male reader is often portrayed as something that has to overcome many obstacles, whether it be social status differences or her own past actions.