Well, often in these fanfics, a major plot twist is the technology or magic system. In the RWBY universe, Dust is important. But in the alternate universe, it could be that Dust has no power, or it has some completely different and unexpected effect. And the semblances of the characters might change drastically. Say, Yang's ability to absorb damage and use it as strength could turn into something like the ability to heal others instead. And then there's the world - building aspect. The alternate universe could be a post - apocalyptic wasteland instead of the somewhat civilized world we see in RWBY, which would be a huge plot twist for the characters to deal with.
Well, at first, the characters would be in shock. But then, Ruby would step up. She's adaptable, so she'd start learning about the new rules of combat, the types of Grimm or other threats in this alternate universe. Yang would be a bit more brash. She might get into some fights to test the waters. Weiss would be analyzing everything from the political systems to the economic structures. She'd try to find a place where she could use her family's influence (if there's an equivalent in the new world). Blake would be on the lookout for any signs of oppression, especially if the Faunus situation is different. She'd also be the one to make sure the group doesn't do anything to offend the local cultures. All in all, they'd have to learn new fighting styles, new languages, and new ways of interacting with others.
One interesting concept could be the different versions of the characters in the alternate universes. For example, a Ruby in a steampunk - themed alternate universe might have a different weapon design and fighting style. Another concept could be how the relationships between the characters change. Maybe in one alternate universe, Weiss and Blake are bitter enemies instead of friends. Also, the alternate universes could have different rules for Dust, which would lead to unique battles and power - ups.
One possibility is that the relationships between the characters are altered. Weiss might find that in this parallel universe, she has a closer bond with someone she was not as close to in her own universe, like Blake. They would have to adapt to these new relationship dynamics while also trying to figure out how to get back to their own universe if that's their goal.
It could be alternate versions of the villains from their own universe. For instance, an alternate Voldemort who is even more powerful. Maybe there are also new characters who oppose Harry and Teddy just because they are outsiders in this alternate universe.
In this fanfic, they might encounter alternate versions of themselves. For example, Harry could meet a version of himself who is a dark wizard instead of a hero. Teddy, with his shape - shifting ability, could have a hard time adjusting to the new universe where the rules of magic might be different. They may also find new magical creatures that don't exist in their original universe and have to figure out how to interact with them.
Writers can start by thoroughly understanding the original RWBY universe. Know the characters, their personalities, and the lore. Then, when creating the alternate universes, make bold changes. For example, change the color - based power system to something else unique. Also, focus on the emotional journey of the characters. If they're in a strange new universe, how do they feel? Are they scared, excited, or confused? This will draw readers in.
In a fanfic where Summer Rose is alive, the plot could center around her teaching Ruby and Yang new combat techniques and strategies. She could also introduce them to a network of Huntsmen and Huntresses that she has been a part of. This would lead to new adventures and battles. Perhaps she takes them on a journey to a far - off land where a new type of Grimm has been discovered, and they have to work together to figure out how to defeat it.
Weiss's Glyphs might work in a completely different way. For instance, instead of using them mainly for ice and summoning, they could be more focused on other elements like fire or electricity in the parallel universe. This would force her to relearn how to use her powers effectively.
In RWBY alternate universe fanfiction, a cool idea is that the characters switch roles. Yang could be the shy, bookish type while Weiss is the brash, party - loving one. Also, the Dust element could be completely different. Instead of being a resource mined from the earth, it could be something that is created through magic. Additionally, an interesting concept is an AU where the characters are in a modern, non - combat setting, like a high school drama where they still have their unique personalities but deal with normal teenage problems.