The setting is a common element too. When Ranma crosses over into a different world, the new setting affects his actions and the overall story. For example, if he crosses over into a post - apocalyptic world, he has to use his martial arts in new ways to survive. And of course, the humor that is characteristic of Ranma 1/2 often gets transferred and combined with the humor (if any) of the crossed - over universe.
One common theme is the interaction between the unique characters from Ranma and the world of Pokegirls. For example, how Ranma's martial arts skills might be used in the Pokegirls' universe. Another could be the exploration of different genders, as in Ranma's curse, in the context of Pokegirls.
Adventure is also a common theme. Picture Ranma traveling through the Pokemon regions, facing different Gym Leaders and trainers. He would bring his martial arts expertise into the Pokemon battles, which would be a new and exciting take on the typical Pokemon adventure.
One common theme is the clash of different worlds. Inuyasha is set in a feudal era full of demons and magic, while Ranma has a more modern (but still very Japanese - culture - influenced) world with martial arts and strange curses. So when the two are crossed over, the difference in their worlds often leads to interesting plotlines. Another theme is the interaction between the characters. For example, Inuyasha's brash and impulsive nature vs Ranma's own quick - tempered but also comical personality can create a lot of humorous and tense situations.
One common element is the combat aspect. In Ranma 1/2, there are all kinds of martial arts battles, and in RWBY, there are intense battles with weapons and semblances. This makes for great fight scenes when combined in a crossover. For example, Ranma could use his martial arts skills against Grimm in RWBY.
Friendship is also a big theme. Since both Ranma and Naruto value friendship highly in their original series, in the crossovers, they usually form a strong bond. They learn from each other's strengths and support each other in facing various challenges.
Often, there are themes related to identity. Ranma's dual - gendered nature can lead to stories about how he reconciles his male and female selves, especially in romantic or sexual situations as seen in lemon fanfictions. There may also be themes of jealousy or competition among the characters who are interested in either male or female Ranma.
One common theme is the clash of different worlds. Ranma 1/2 has a more martial - arts - based world, while Tenchi Muyo is more sci - fi. So, in crossovers, you often see how these two different types of worlds collide. Another theme is the exploration of new powers. Characters from both series might discover new abilities when they interact.
One common theme could be the challenges of the female Ranma dealing with pregnancy in a crossover universe. Maybe she has to adapt to different cultures or magical elements from the crossover.
How about a Ranma crossover with Harry Potter? Ranma could be a foreign exchange student at Hogwarts. His martial arts could be a form of magic in the wizarding world. Or a crossover with Fullmetal Alchemist. Ranma might get involved in the search for the Philosopher's Stone or help the Elric brothers with their alchemical problems. There are so many possibilities for Ranma crossover fanfiction.
Another issue is the power scaling. If you cross Ranma 1/2 with a series like One Piece where the characters have superhuman abilities, you need to figure out how Ranma's martial arts stack up. You don't want to make him too overpowered or too weak compared to the new characters he's interacting with.