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.
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.
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.
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 Harry making new friends in Salem who have different magical abilities than those he knew in Hogwarts. Another could be him encountering a unique magical creature native to Salem. Maybe he gets involved in a mystery related to an old Salem witch trial that has some lingering magic.
Explore her relationships. She could have a complex relationship with Salem, loving her mother but hating her actions. And with the RWBY characters, she could start as an enemy but gradually become an ally. By developing these relationships, her character can become more multi - dimensional. For example, her friendship with Blake could start with distrust but grow into a strong bond as they share their stories of being different from their families.
One idea could be a story where a new student arrives at Salem School with a mysterious power that has connections to the wizarding world of Harry Potter. This power could draw the attention of both good and bad forces within the Salem School community.
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.
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.