One possible plot twist could be that RWBY initially believes Salem's motives are good. Since she raised them, they might be blind to her true evil nature at first. For example, Salem could have presented herself as a protector against some other greater threat, making RWBY question their newfound allies when they start to oppose Salem.
Perhaps a major plot twist could be that Salem raised RWBY with the intention of them being her ultimate weapons against the Gods. She could have been grooming them to carry out her revenge, but RWBY discovers this plan and has to struggle with their loyalty to Salem who was like a mother to them, and their sense of right and wrong.
One possible plot twist could be that the characters raised by Grimm end up being the ones to save the RWBY world. Despite their upbringing, they develop a sense of justice that is different from the norm. Another could be that they have a hidden power that is related to their Grimm - raising, which gives them an edge over the regular Grimm.
Well, it could be about Si somehow getting transported into the RWBY world and gradually taking on the characteristics and powers of Salem. Maybe Si starts to influence the existing power dynamics in the RWBY universe, causing chaos among the various factions like the Huntsmen and the Grimm. For example, Si could start to manipulate some of the characters, using knowledge from the real world to outwit them and further Salem's goals, even if it's unconsciously at first.
One possible plot twist could be that Gohan becomes more powerful than Vegeta much earlier than expected. This would create an interesting dynamic as Vegeta would have to deal with his student surpassing him. Another could be that Gohan discovers a new Saiyan ability that Vegeta was unaware of, which could change their relationship and how they approach training.
One possible plot twist could be that Naruto gains unique fire - related powers from the phoenix. Since the phoenix is often associated with fire in many mythologies, Naruto might be able to control a different kind of fire jutsu, which would set him apart from his normal abilities in the original Naruto story.
Perhaps Naruto's relationship with the other ninja in Konoha is affected. Since Yoruichi has a different set of values and skills compared to the traditional Konoha ninja, Naruto could be seen as an outlier. This could lead to some initial misunderstandings and later, a new form of respect from his peers as they see the effectiveness of his unique upbringing.
One plot twist could be that Hermione discovers she has a hidden connection to the Malfoy family, like she's a long - lost relative. This would add a whole new layer to her being raised by them. Another could be that she uses her knowledge of both the Gryffindor and Malfoy ways to broker peace between the two factions in the wizarding world that are often at odds. Maybe she uncovers a secret plot within the Malfoy family that goes against her new - found loyalty to them, forcing her to choose between her upbringing and what she believes is right.
One possible plot could be that Harry Potter, after some sort of magical accident or portal opening, ends up in the world of RWBY. The RWBY characters, perhaps Ruby herself, find him as a baby or young child and decide to raise him. Harry would grow up learning about the Grimm and Huntsmen, while also having his own magical abilities. This could lead to some interesting combinations in combat, like using magic along with a weapon like Crescent Rose.
Well, it could involve Ruby being influenced by an evil force in this fanfic. Maybe she's taught dark magic or has her moral compass twisted. For example, she might start seeing the world in a more cynical way and use her powers for less noble purposes.
Perhaps a plot twist would be that during the fight, Tai discovers a secret about Raven that completely changes his perception of her. For example, he finds out that she has been working undercover to stop a greater threat all along, and their fight then turns into a reluctant alliance against a common enemy.
One possible plot twist could be that Adam has a hidden weakness that Sun discovers during the fight. Maybe it's related to his past or his weapon. Another could be that Sun is actually being controlled by an outside force and Adam has to decide whether to take advantage of it or help him.