One common theme is identity. Ruby has to figure out how being a princess fits into who she is, as she's always seen herself as a Huntress. Another theme is responsibility. With princess status comes new duties, like ruling or representing a kingdom. Also, friendship often plays a role. Her friends might have to adjust to her new status, and she might rely on them in her new royal life.
Yes, there are several out there. You can start by looking on popular fanfiction websites like Archive of Our Own. Just search for 'RWBY Ruby is a Princess' and you'll likely find a good number of fics. Some might focus on Ruby's new role as a princess in an alternate universe, with her having to deal with royal duties while still being the Ruby we know from the show, with her combat skills and her love for her friends.
One possible plotline could be that Ruby discovers her hidden princess heritage and has to balance her normal Huntsman duties with the newfound responsibilities of royalty. Maybe she has to attend grand balls and diplomatic meetings while still trying to fight Grimm. Another could be that she has a secret princess identity that she uses to infiltrate an enemy kingdom or group, using her charm and skills as Ruby as well as her new royal persona.
This secret would likely make Ruby more self - conscious at first. She's used to being just a normal girl with a big dream. Now, she has to deal with the expectations of being a princess. However, over time, it could make her more confident as she learns to embrace both sides of herself. She might become more of a leader, not just in battle but also in diplomatic situations. For instance, she could use her princess status to form alliances between different groups in Remnant.
Ruby could be anyone. It might be a name given to a character in a specific story or just a name of a person in real life who likes to read stories in her own time.
The Pokémon special, Ruby, was a fictional story created by Japanese manga artist Hiroko Hanami in 1997. The story was about an elf named Ruby who was learning Pokémon knowledge and skills in a mysterious Pokémon training class. Ruby gradually became a powerful Pokémon Master and worked with his Pokémon companions to protect the world from the threat of evil forces.
Well, her sister Yang would definitely be one of the main characters. Yang would be very protective of Ruby and would try to help her in any way she could. Weiss would also be important. She might use her intelligence and Dust - related skills to assist Ruby. And Blake, with her stealth and combat skills, could be crucial in protecting Ruby and guiding her through difficult situations.