What could happen in a 'underfell sans meets underswap fanfiction'?

In such a fanfiction, there could be a lot of conflict. Underfell Sans is from a more hostile AU than Undertale. He might initially be distrustful when meeting the characters from Undertale. For example, he could misunderstand their kindness as weakness or a trick.

One possible plot twist could be that Underfell Sans turns out to be a long - lost relative of one of the Underswap characters. Another could be that a villain from Underfell follows him to the Underswap world and causes chaos. Or perhaps Underfell Sans is actually there to steal something important from the Underswap world but has a change of heart halfway through.

Another scenario could be that there's immediate conflict. Sans might suspect that this different - looking Chara has some malicious intent towards his world or his friends. So he could start a fight right away. But as the encounter progresses, they might start to understand each other better and the fight could turn into a more of a philosophical debate about the nature of their respective worlds and the actions they've taken in the past.

Another theme is friendship or partnership. They often come together to face challenges in the Underground. For example, in many fanfictions, they join forces to defeat a powerful monster or solve a mystery that threatens their world. This theme of unity despite their differences is really appealing.

The contrast between the two characters. Underswap Sans is more laid - back and friendly compared to Underfell Sans who is more rough and edgy. When they interact in fanfictions, it creates a lot of interesting dynamics, like how they might clash or gradually understand each other.

Characterization is key. A good fanfic should accurately portray the personalities of both Underswap Sans and Underfell Sans. Their unique traits, like Underswap Sans' more positive and friendly nature compared to Underfell Sans' tougher exterior, should be well - presented.

One common theme is friendship. Despite their differences from different AU's, they often form a unique bond.

You can start by looking on Archive of Our Own (AO3). It has a large collection of fanfictions for various fandoms, including the Undertale AU crossovers like Underswap Sans x Underfell Sans. Another place could be Fanfiction.net, though the quality may vary more there. Additionally, Tumblr sometimes has users sharing or recommending such fanfictions in the Undertale fandom tags.

One common theme is the exploration of differences. Underfell sans and underswap papyrus are from different universes with distinct personalities. Fanfictions often focus on how they deal with these differences, like underfell sans's more aggressive nature compared to underswap papyrus's more positive and energetic self.

There's a really cool fanfic called 'FellSwap Encounters'. It delves deep into the relationship between underfell sans and underswap sans. It starts with a chance meeting and then shows how they gradually understand and support each other. The author does a great job of showing their different characteristics and how they complement one another.