One great 'underfell sans fanfiction' is 'A Darker Path'. It really delves into the darker aspects of Underfell Sans' character. Another good one could be 'Underfell Sans: Redemption'. It shows his journey towards a more positive change. And there's also 'The Underfell Sans Chronicles' which has a really interesting plot that keeps you hooked from start to finish.
Well, 'Soul of a Monster' in the 'underfell sans fanfiction' genre is quite engaging. It explores the internal struggle of Sans in that universe. 'Fell for You' is a fan favorite as it has a unique take on Sans' relationships. Also, 'Underfell Sans: The Hidden Truth' reveals some secrets about his past that make for a fascinating read.
Well, in the world of 'underfell sans abuse fanfiction', 'The Abyss Within' stands out. It has a very detailed description of the abuse scenario and how Sans endures it. This fanfiction is not for the faint - hearted as it gets quite intense. Additionally, 'Hope in Desolation' is also a great read. It shows the glimmer of hope in Sans's life despite the abuse he has faced, and the way the author develops the story is really engaging.
One great 'underfell sans x reader fanfiction' is 'A Dark Encounter'. It has a really interesting plot where the reader is thrown into the Underfell universe and has to navigate their relationship with Sans. The story is full of tension and character development.
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.
There's also 'Sibling Rivalry Reimagined' which delves deep into how their personalities from their respective universes interact. It has some really interesting character development for both Sanses. It shows how their differences can lead to both conflict and unexpected understanding. The author does a great job of portraying their emotions and the way they communicate, which is quite different from the original game's interactions.
A plot could revolve around an accident that causes their universes to merge partially. Underfell Sans and Sans find themselves in a strange new reality where they have to figure out how to get back to their own universes. Along the way, they learn about the differences and similarities in their lives, and this leads to some really interesting character development.
One popular 'baby underfell sans fanfiction' is 'The Tiny Terror'. It has an interesting take on the character in a baby form, with unique plot twists and character interactions.
Frisk would be a likely candidate. Since Frisk is the main character in Undertale and has a very adaptable personality. They could approach Underfell Sans with an open mind and try to understand him.
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 could be the exploration of Sans' struggle to overcome the abuse. Another might be the relationships he forms with other characters in the face of such a difficult past. Also, the impact of the abuse on his personality and actions is often a theme.
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.