Well, you could do a fusion fanfic where the characters fuse due to some ancient magic or a powerful relic. Maybe there's a relic that when activated, causes two characters to fuse together. You could have a plot where the fused characters have to figure out how to control their new powers and how to separate themselves. And they might face challenges that only their combined abilities can overcome, like fighting a super - powerful Grimm that normal teams can't handle.
A cool concept for an RWBY fusion fanfic is to fuse characters from different generations. Say, fuse a current - day character like Jaune with a character from the past, like one of the great heroes in the RWBY lore. This could lead to interesting storylines where the modern - day values and fighting styles clash and blend with the old - school ways. The fused character would have to adapt and use the best of both worlds to face the threats in the RWBY universe.
One idea could be that Bulma discovers a new technology that allows her to fuse with different characters' minds, not just their bodies in a traditional sense. She could fuse with Goku to understand his pure love for fighting and gain some of his combat instincts.
One idea could be a fanfic that explores the backstories of minor characters in RWBY more deeply. For example, you could focus on a character like Velvet and create a story about her training before coming to Beacon. Another could be a crossover within the RWBY universe itself, like a team-up between different schools' teams that we haven't seen much of in the official series.
One idea could be a fusion between Deku and All Might. Imagine Deku having not just One For All, but also All Might's combat experience and charisma from the start. It would change the dynamic of his battles and his relationships with other characters. Another idea is fusing Todoroki with a water - based hero, which could enhance his ice and water abilities even more and lead to new and creative ways of using his quirk in combat and rescue situations.
One idea could be that the Incredibles' superpowers are enhanced by the Avengers' technology. For example, Mr. Incredible could get a high - tech suit from Stark Industries that gives him even more strength and the ability to fly short distances. Another plot could involve the villains from both universes teaming up, forcing the combined heroes to work together in new ways. Maybe Syndrome teams up with Loki, and they create a device that can nullify superpowers, so the heroes have to find a way to stop it.
One idea could be to explore an alternate origin for the characters. For example, what if Ruby's silver eyes were a result of a prototype experiment gone wrong? Another could be to set the fanfic in a parallel universe where the Grimm are actually created by a mad scientist using prototype technology. And perhaps a story where the characters have to use prototype weapons that have unpredictable powers.
One idea could be exploring new stand abilities inspired by RWBY characters' weapons or semblances. For example, a stand based on Ruby's Crescent Rose could have the ability to manipulate time briefly like Ruby can move at high speeds. Another idea is to create crossovers within the RWBY universe using stands, such as having a stand user from a different part of Remnant interact with the main RWBY team and their battles.
For a 'rwby breeding fanfic', you might look at the idea of cross - species breeding if there are non - human characters in RWBY. Maybe a Faunus character breeds with a human - like character. This could bring up all sorts of interesting cultural and physical differences in the offspring. The fanfic could explore how the society in RWBY reacts to such cross - breeding, whether there is acceptance or discrimination, and how the characters themselves deal with the consequences of their actions.
You could base the fanfic on a quest. The RWBY team is hired by a DND - like noble to retrieve a powerful artifact. This artifact could be something that has the power to change the balance in Remnant (the RWBY world). Along the way, they encounter classic DND monsters like dragons and beholders. They also meet different DND races, such as elves and dwarves, and have to form alliances. Ruby might be the leader in this quest, using her quick thinking and charisma, while Weiss uses her knowledge of magic and lore to figure out clues.
One idea could be exploring the backstories of minor characters in more depth. For example, you could focus on a character like Velvet and her experiences at Beacon Academy before the main events of RWBY. Another idea is to create an alternate universe where the Dust technology has different properties or uses. Maybe in this AU, Dust can be used to create temporary portals to different locations.
A prequel could center around the formation of the different kingdoms. Explore the political tensions and alliances that were made. You could also show how the Dust was discovered and how it became such an important resource. This would give readers a better understanding of the world of RWBY before the events of the main series.