Well, 'rwby fallout fanfic' is likely a fan - created story that combines the elements of RWBY and Fallout. It might have RWBY characters in a post - apocalyptic Fallout - like setting, with new adventures, challenges, and perhaps some unique takes on the powers and personalities of the RWBY characters within this different world context.
I'm not sure if there are a whole lot of these fanfictions, but you might want to check out fanfiction.net. Just search for 'Fallout New Vegas Lone Courier x RWBY' and you'll likely find some. Some might be a bit rough around the edges in terms of writing quality, but there could be some hidden gems.
A more complex plot might be that there is a dimensional rift that is causing chaos in both universes. Characters from both Fallout New Vegas and RWBY have to work together to close the rift. In the process, they learn about each other's worlds, values, and fighting styles. The contrast between the post - apocalyptic technology and magic - based abilities in RWBY could lead to some really interesting interactions and story developments.
The redemption trope can be seen too. Maybe the Courier has some past mistakes or a dark history from Fallout New Vegas, and in the RWBY world, they find a chance to redeem themselves. This can be a really deep and emotional trope, as the Courier tries to become a better person while interacting with the more idealistic characters in RWBY.
I'm not sure specifically which 'rwby fallout fanfic' stories are the most popular. However, often the ones that gain popularity are those that do a great job of integrating the two universes seamlessly. They might have really interesting plot twists, like a RWBY character forming an unexpected alliance with a Fallout faction.
Another theme is adaptation. RWBY characters are used to their own world, and when thrown into the Fallout world, they need to adapt to new technologies, cultures, and threats. This creates a lot of interesting character development and story arcs. For example, Ruby might have to learn how to use a Pip - Boy or deal with the different types of mutants in Fallout.
Many fanfictions in this crossover focus on the cultural shock aspect. The Lone Courier comes from a post - apocalyptic world full of mutants, raiders, and survival challenges. When they enter the RWBY universe, which has its own set of rules, cultures, and threats, there are a lot of opportunities for humorous and also thought - provoking interactions as the Courier tries to understand and navigate this new world.
Cait from Fallout New Vegas and Yang from RWBY would be a fiery pairing. Cait is tough, strong - willed, and has a bit of a temper, much like Yang. They could have some great sparring sessions where they exchange fighting techniques. Their personalities might clash at first, but they would also learn from each other. Cait could learn about the importance of family from Yang, and Yang could pick up some of Cait's more street - smart survival skills. This pairing would lead to a lot of interesting character development and some really fun and intense scenes.
RWBY's reactions could vary greatly. Yang would probably be excited about the action - packed parts of the fanfiction. She loves a good fight, and Fallout often has intense combat scenes. Ruby would be drawn to the unique characters, especially those with special powers or abilities. Weiss might be more interested in the social hierarchies and how they function in the Fallout world. And Blake could be thinking about how the stories in the fanfiction could be used to teach lessons about coexistence and conflict resolution in her own world.
One idea could be a crossover where characters from Fallout enter the RWBY universe. For example, a Vault Dweller could end up in Vale and have to adapt to the Grimm - filled world while also trying to find a way back home. Another could be a story where RWBY characters are thrown into a post - apocalyptic setting like in Fallout, dealing with radiation and mutated creatures.