Well, it could be really interesting. Maybe it shows a unique interaction between Chara from Storyshift and Sans from Undertale. Their personalities are quite different. Chara can be rather complex and Sans is known for his laid - back yet perceptive nature. So in the fanfiction, there might be a lot of unexpected exchanges and development of their relationship.
Chara is often a popular character. Their complex nature makes them interesting to explore in the context of Storyshift. They can be portrayed in different ways, sometimes more sympathetic than in the original Undertale.
You should begin with a clear idea of what makes your Undertale AU different. Develop interesting character backstories and interactions. And make sure the dialogue is engaging and fits the tone of the comic.
One interesting plot twist could be the role reversal of characters. For example, if a typically heroic character becomes more of an anti - hero or vice versa. It completely changes the dynamics of the story.
Another plotline could be that there is a rift in the multiverse, and Chara and Sans are brought together to fix it. Along the way, they discover things about each other's universes and themselves, and in the end, they manage to close the rift and return to their respective worlds with a new understanding of the multiverse.
Well, they might see different versions of characters from Undertale. For example, the RWBY characters could be really surprised by the unique battle mechanics in Undertale's AU multiverse. Maybe Ruby would be especially interested in the different types of weapons or magic used in that world.
Blake could also be a great character to focus on. Given her own complex backstory and her tendency to be more introspective, she might have deeper insights into the characters and situations in the Undertale AUs. She could form unique relationships with some of the more morally ambiguous characters in the Undertale multiverse.
An AU fanfic is a type of fan fiction where the story takes place in an alternate universe with different settings or circumstances than the original work.
An au fanfic is a type of fan-written story that takes the characters or setting of an existing work and places them in an alternate universe or situation that differs from the original.