Sure. You can check out platforms like Archive of Our Own (AO3). Look for the 'underfell sans x frisk' tag and then filter out the works that are marked as inappropriate or lemon. There are often many well - written, family - friendly fanfics that explore their relationship in different ways, such as adventure - based stories where they team up to face challenges in the Underground.
Sure. There are quite a few. In these fanfictions, the interactions between Underfell Sans and Frisk can be really interesting. For example, they might start off as distrustful of each other since the Underfell world is more hostile. But as the story progresses, they learn to rely on one another. It could be that Frisk's kindness starts to break through Sans' tough exterior in this version of the story.
One plot idea could be a redemption arc for Underfell Sans. Frisk could be the catalyst for his change, helping him to see a different way of living in the Underground. For example, Frisk might show him acts of kindness that he's not used to, and this could start to break down his tough exterior.
One popular theme is redemption. Underfell Sans is often portrayed as a more 'evil' or at least morally grey character compared to the regular Sans. So, stories might focus on his journey towards redemption with Frisk's help. Another theme is survival. Given the harsh nature of the Underfell world, they often have to fight for survival together.
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.
You can start by looking on fanfic platforms like Archive of Our Own (AO3). It has a large collection of Undertale - related fanfics, including those about Underswap Sans and Underfell Sans. Just use the search function and type in the relevant tags.
One popular 'underfell sans x underswap sans fanfic' is 'Twisted Bonds'. It explores their relationship in a really interesting way, with great character development.
A common theme is the exploration of differences. Since they are from different universes, their personalities and ways of life are different. Fanfics often focus on how they deal with these differences.
The writing style is crucial. A good fanfic will have smooth and engaging prose. It won't be full of grammar and spelling mistakes. For this pairing specifically, the interactions between the two should be believable. They come from different 'universes' within the Undertale multiverse, so how they react to each other's differences and similarities can make or break the story. Also, a bit of humor or emotional depth can really enhance the fanfic.