One interesting story could be about the characters' reactions to different timelines. For example, Sans might react in a unique way when faced with a timeline where everyone is overly aggressive. Another could be the reactions of the monsters to human technology that they've never seen before, like a smartphone. And there could also be stories about how the characters react to fan - made scenarios, such as a 'what if' situation where Asriel didn't turn into Flowey.
Sans is one of the most commonly written characters. His laid - back yet mysterious nature makes for interesting reactions. Papyrus is also popular as his over - the - top and positive personality gives a lot of room for different reactions. Frisk is often included too, as they are the main character through which a lot of the game's story is told, so their reactions to various in - game events are frequently explored in fanfiction.
In undertale error x ink fanfiction, a prevalent theme is the power struggle. Error has his own power set and Ink has his. How they use their powers in relation to each other is often explored. Additionally, the theme of identity is present. Both characters have distinct identities and the fanfictions may show how their relationship affects or challenges their individual identities. For instance, Error may question his role as a destroyer when he gets closer to Ink, who is all about creation.
From Undertale, characters like Sans or Frisk could be main characters too. Sans, with his laid - back yet intelligent nature, could provide a great contrast to Error Sans. And Frisk, being the human with the ability to reset and change the course of events, would be crucial in any plot involving the two different universes colliding.
Maybe it's about the characters from Undertale trying to understand Error Sans. Error Sans is a complex character with his own motives and backstory. In the fanfiction, the Undertale characters could be trying to figure out why he is causing disruptions and if there's a way to coexist with him. This could involve a lot of character development and exploration of different moral stances.
Frisk and Chara have a complex relationship already in Undertale. When Error enters the picture, it gets even more interesting. Frisk might be the mediator between Chara and Error. Chara could be hostile towards Error initially, seeing him as a threat to their own existence or plans. Error would likely be dismissive of both of them at first, thinking they are just insignificant parts of a world he might want to destroy.
In the fanfiction, they might meet in a strange, distorted part of the Void. Sans could be his usual laid - back self at first, but then realize the seriousness of Geno's situation. Geno could share some of his past experiences with Sans, which would make Sans more empathetic. And they could start to form an unlikely friendship. They might also exchange some of their unique abilities or knowledge, which could be crucial for the development of the story.