Perhaps Salem discovers a way to use Naruto's chakra for her own evil purposes. So, Naruto has to find a way to stop her while also dealing with the new and unfamiliar world of RWBY. He might learn some new skills from the RWBY characters along the way.
A cool plot could be that Naruto is a long - lost relative of a character in RWBY. Salem senses his power and tries to manipulate him into joining her side. But Naruto, with his strong sense of justice, refuses and instead rallies the RWBY crew to fight against Salem. He could introduce some of his ninja techniques to the RWBY team, like the substitution jutsu which could be very useful in battles against Salem's forces.
Maybe Salem's daughter has unique powers that are different from her mother's. She might struggle to come to terms with these powers and whether to use them for good or evil. For example, she could have the power to heal, which is the opposite of Salem's destructive nature, and she has to decide if she'll use it to counter her mother's actions.
One idea could be exploring their past relationship in more detail. Maybe a time when they first met and how their initial trust or distrust formed.
One idea could be Salem's reaction to the powers and technology in the Worm universe. Maybe she tries to use some of the parahuman abilities or advanced tech to further her own goals in the RWBY world.
One idea could be Ruby trying to understand Salem's motives beyond just destruction. Maybe she discovers that Salem has a tragic past that led her to this path and Ruby attempts to find a way to redeem her. Another plot could involve Salem targeting Ruby specifically because of her silver - eyed powers and Ruby having to outwit Salem in a series of battles.
Another plot could involve a RWBY character ending up in the Naruto universe. Say, Weiss gets sent to Konoha. She might initially struggle with the different culture and the use of chakra, but eventually she could use her Glyphs in unique ways by combining them with chakra. This could also lead to some interesting interactions between her and the ninja students there.
Perhaps in this fanfiction, Weiss discovers a strange portal and steps through it, ending up in the Naruto world. She meets Naruto and is intrigued by his ninja abilities. They could start training together, with Weiss learning some ninja techniques and Naruto learning about Dust. Their combined skills could then be used to protect Konoha from a new threat that has some similarities to the Grimm from her world.
One idea could be that Naruto and his friends get transported to the RWBY world. They team up with Ruby and the gang to fight a common enemy that combines the threats from both universes, like a group of powerful ninja - Grimm hybrids.
One idea could be a crossover where Naruto somehow ends up in Salem's world and has to use his ninja skills to survive in a new and magical environment. Another could be a story where Salem gains the ability to use chakra and tries to take over the Naruto world. Or perhaps a story where Naruto and Salem team up against a common, even greater enemy.
Well, a 'naruto x rwby fanfic' could center around a training arc. Imagine Naruto training the RWBY team. He could help Ruby improve her speed and combat skills by teaching her some of his ninja movement techniques. Yang could learn from Naruto how to better control her temper during battles, similar to how Naruto had to control his Nine - Tails' chakra. Meanwhile, the Naruto characters could also be learning about the Grimm and how to fight them. They could incorporate their ninja tools and jutsu to combat these new and strange enemies from the RWBY world.
Well, a possible plot for 'naruto in rwby fanfiction' is that Naruto is mistaken for a new type of Huntsman. He then has to prove himself in the Beacon Academy. Along the way, he befriends Team RWBY and Team JNPR. He could introduce his ninja techniques to combat classes, and they could incorporate some of his strategies into their own fighting styles. For example, Weiss could use Naruto's ability to walk on water to create new ice - based attacks.