Well, one interesting idea could be exploring the backstories of minor characters more in - depth. For example, we could learn about the childhood of a random student at Beacon Academy, how they got their weapon, and what led them to enroll there.
Some fanfictions might focus on alternative storylines. Like, what if Ruby didn't pick up Crescent Rose? How would her journey change? It could also explore different relationships between the characters. Maybe Weiss and Blake become closer friends much earlier than in the original, and how that would affect their team dynamics.
One interesting idea could be a crossover of different timelines within RWBY. For example, characters from the past meet the current ones and have to deal with the differences in their worlds. Another could be a crossover of different teams in unexpected ways, like Team RWBY having to team up with a rival team to face a common enemy that is more powerful than any they've faced before. And sometimes, there are crossovers that involve alternate versions of the characters, where their personalities or abilities are slightly different, which can lead to very unique and engaging storylines.
One idea could be a crossover where a character from RWBY gains the powers of Dishonored's Corvo. They could use the blink ability to quickly dodge attacks in battles against Grimm. Another idea is to have a setting where the world of RWBY is affected by the plague from Dishonored, and the characters have to find a cure while dealing with political unrest.
One idea could be a crossover where The Punisher teams up with RWBY characters to take on a new, powerful criminal organization in Remnant. He could bring his unique combat skills and no - nonsense attitude to the mix.
One idea could be to explore a crossover between RWBY and Darkwatch characters. Maybe Ruby could team up with a Darkwatch hunter to fight a new kind of Grimm that has some vampiric abilities. This would create a really unique dynamic as they combine their different fighting styles and powers.
One idea could be focusing on team strategies for different combat scenarios in RWBY. For example, how Team RWBY might plan to take on a powerful Grimm that has unique abilities. Another could be about the strategic use of Dust in battles, like creating new combinations or ways to deploy it for maximum effect. And a third idea could be exploring the strategic alliances and rivalries between different teams at Beacon Academy.
One idea could be to have Ainz Ooal Gown from Overlord end up in the RWBY world. He could be seen as a powerful new force, and his magic and strategic mind would create a lot of interesting scenarios. Maybe he'd form an alliance with one of the academies, or be seen as a threat by Salem and her forces.
An OC in RWBY fanfiction could be a character who is a master of stealth. They could use their skills to gather intelligence for the teams at Beacon Academy. Their backstory could involve growing up in a family of thieves, but they decided to use their abilities for good. They might have a Semblance that allows them to become invisible for short periods of time, but it has a drawback like draining their Aura quickly. This OC could interact with characters like Blake, who also has some stealth - like abilities, and they could learn from each other.
For RWBY OC fanfiction, you could make an OC who has the power to manipulate time on a small scale. This would be a really cool ability in battles, being able to slow down opponents or speed up oneself. Another idea is to have an OC that is a faunus with a very rare animal trait, like a phoenix - like faunus. Their story could revolve around hiding their true nature because of discrimination. And an OC that is a transfer student from a far - off land with a completely different fighting style compared to the students at Beacon Academy would also make for an exciting story.
Another interesting idea is a story where a RWBY character discovers they have latent wizard powers. Ruby, for instance, could find out she has wizard abilities on top of her scythe skills. This could lead to a new arc in her character development as she tries to balance and master both her combat skills and newfound magic. It would also open up new storylines with her team and the other characters.
One interesting idea could be the RWBY characters having to team up in new ways to combat the kaiju. For example, Ruby's speed might be used to quickly dodge a kaiju's attacks and find its weak spots. Another idea is the fusion of Dust technology with kaiju - like elements. Maybe they create new weapons that can both harm the kaiju and also harness some of their power. Also, the idea of kaiju having Aura or semblances of their own could be really cool, changing the dynamics of how the RWBY characters interact with them.