One idea could be a crossover where Cinder somehow gets transported to the Naruto universe. She might initially try to use her powers to gain control, but then realizes she has to adapt to the new chakra - based powers. Meanwhile, RWBY characters could also end up in the Naruto world in search of Cinder and end up forming unexpected alliances with Naruto and his friends.
Perhaps in a fanfiction, a new villain emerges that poses a threat to both the RWBY world and the Naruto world. Cinder, having her own goals but also realizing the greater danger, teams up with RWBY and Naruto characters. They would need to combine their different abilities like Naruto's Rasengan and RWBY's weapon - based combat along with Cinder's fire - based powers to defeat this new common enemy.
Another possibility is a story in which a character from RWBY is sent to the Naruto world and then later ends up in the Overwatch universe. They could bring their unique combat style and start training with the different groups in each world, like learning ninjutsu in Naruto and using advanced tech in Overwatch.
One idea could be a crossover where a character from RWBY discovers the ability to use Mokuton. They might struggle at first to control it, like Naruto did. Maybe they could use it to create unique weapons or defenses in the RWBY universe.
A possible fanfiction could be about the origin of the Rinne Sharingan having some connection to the world of RWBY. Maybe there was an ancient civilization in RWBY's past that had a similar power, and through some sort of dimensional rift, it influenced the development of the Rinne Sharingan in Naruto's world. This would involve a lot of world - building and exploration of both universes' histories.
One idea could be to have the characters from RWBY travel through a stargate to the Pegasus Galaxy where Stargate Atlantis is located. They could encounter the Wraith and have to use their unique abilities from Remnant to fight them. For example, Ruby's speed and Crescent Rose could be very useful in combat against the Wraith.
A possible fanfiction could involve Kiryu's memories of Godzilla influencing the RWBY characters. For example, Godzilla's tenacity and will to protect could inspire Ruby and her team. They could learn from Kiryu's combat techniques and use them against the Grimm. And perhaps Kiryu could be repaired and upgraded using RWBY's technology.
One idea could be that Captain America is somehow transported to the RWBY universe. He could team up with Team RWBY to fight against the Grimm. His shield would be a unique weapon in that world, and his leadership and combat skills would be highly valuable.
One idea could be to have the characters from RWBY end up in the world of Final Fantasy 15. For example, Ruby could meet Noctis and they could team up to fight some common enemy. Ruby's speed and scythe - wielding skills could be a great addition to Noctis' combat style.
A fanfiction could also explore the idea of the Far Cry 5 characters getting some of the powers from RWBY. The Deputy could gain Ruby's speed and use it to quickly traverse the map and rescue hostages. The Seed family could be interested in the Dust technology from RWBY and try to harness it for their own evil purposes. This would lead to a conflict where the RWBY characters have to protect their technology while also helping the people of Far Cry 5.
A third idea is to create a fanfiction where the backstories of the RWBY characters are intertwined with the lore of God of War. For instance, Weiss could have a connection to a long - lost civilization in the God of War world that was known for its ice - based magic. This discovery could lead her on a journey to uncover her family's past and also learn more about this new world she's connected to.
Another idea is a time - travel fanfic. Cinder travels back in time and meets a younger Ruby. She could try to manipulate Ruby into following a different path, but Ruby's strong will and sense of justice might resist. This would create a lot of conflict and interesting character dynamics as Cinder tries to change the future and Ruby tries to protect it.