A great concept for 'rwby expansion fanfiction' is to introduce new kingdoms or regions in the RWBY world. Describe their unique cultures, fighting styles, and Dust usage. You could also write about a character from one of these new areas coming to Vale and interacting with the main RWBY cast, bringing with them new knowledge and perspectives.
One interesting idea could be exploring new and unique ways the expansion jutsu can be used in battles. For example, using it not just for physical size increase but also for expanding the range of other jutsus.
One interesting concept could be the expansion of character backstories. For example, delving deeper into Ruby's early days of training before Beacon Academy. Another might be exploring new Grimm species that are more powerful and have unique abilities. Also, the relationships between characters can be further developed, like the friendship between Weiss and Blake, showing their interactions outside of the main plot.
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.