Often, the cuteness of the baby form is a key feature. Despite being from the Underfell universe which is usually more edgy, the baby version brings out a different side.
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.
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.
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.
The fan base loves these characters so much that seeing them interact in new and unexpected ways is always a treat. The relationship between them can be explored in so many different ways, from friendship to rivalry. And the unique art styles and interpretations that often come with these fanfictions add to the overall appeal. There are also some really emotional stories that can be told about them finding common ground or learning from each other, which really tugs at the heartstrings of the readers.
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 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.
Common themes in 'underfell sans x papyrus fanfiction' include power dynamics. Since Underfell is a harsher world, there might be a shift in the power balance between Sans and Papyrus. Additionally, redemption can be a theme. Maybe one of them has made mistakes in this unforgiving world and is seeking redemption. Also, the theme of trust, as they need to trust each other to survive in such a difficult environment.
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.