One idea could be exploring the backstories of the characters during the Great War. For example, how Ruby's ancestors first discovered their powers and how they were used in the war.
Maybe a story about a secret alliance formed during the Great War. The characters from different factions in RWBY coming together for a common, hidden goal. This could involve lots of political intrigue and tense negotiations.
A plot could revolve around the discovery of a powerful, ancient weapon during the Great War. The different sides in the war would then vie for control of it, leading to a series of epic battles. The story could focus on how the main RWBY characters get involved in this struggle and how their relationships are tested.
One idea could be exploring the backstories of minor characters during the Great War. Maybe show how they got involved and what their personal stakes were.
One idea could be Kratos arriving in the RWBY world and getting involved in the fight against the Grimm. His combat skills and Spartan rage would be a huge asset. Maybe he teams up with Ruby and her friends, teaching them some of his more brutal combat techniques.
One interesting plot idea could be exploring the aftermath of the war from the perspective of a young survivor. They might be on a journey to find a rumored safe haven, facing various mutated creatures along the way.
One idea could be a new student arriving at the school with a mysterious power that no one has seen before. This could cause both excitement and suspicion among the other students.
One idea could be a mercenary who is hired by a mysterious client to steal an ancient relic from Beacon Academy. He has to navigate through the various defenses and teams of Huntsmen and Huntresses.
A plot could involve an esports competition where teams from different kingdoms in the RWBY universe compete. The story could explore how the RWBY team overcomes rivalries and strategic differences. They might also have to deal with a mysterious hacker trying to disrupt the tournament.
Well, you could have a story where all the RWBY characters swap their semblances for a day in chibi form. Ruby with Weiss's glyphs, Weiss with Blake's shadow clones, Blake with Yang's strength, and Yang with Ruby's speed. It would lead to some really funny and unexpected situations as they try to go about their normal activities at school. Or perhaps a fanfiction where the chibi RWBY teams are transported to a world made entirely of sweets. They have to resist the temptation to eat everything while also finding a way back home. A third option might be a mystery plot. A valuable item has gone missing in Beacon's chibi - version campus, and the teams have to solve the mystery of who took it and why.
One idea could be a new character arriving at the battlefield with a unique semblance that changes the tide of battle. For example, a character with the ability to manipulate time in a small area, allowing allies to get in extra attacks while enemies are frozen for a moment.
One idea could be Noctis arriving in the RWBY world and having to learn about Dust and how to use it in combat. Maybe he teams up with Team RWBY to fight against a new type of Grimm that his unique skills are well - suited to defeat.
A possible plot for 'rwby the incredibles fanfiction' is that Syndrome from The Incredibles teams up with Salem from RWBY. Syndrome offers his advanced technology to Salem in exchange for her help in getting revenge on the superhero community. The RWBY characters and the remaining Incredibles then have to find a way to stop this unholy alliance. They might start by training together to combine their different skills. Ruby could teach Dash some new acrobatic moves, and Elastigirl could show Blake how to use her flexibility in combat more effectively.