underfell reacts to sans

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.

There's 'Sans - Bound'. This fanfiction focuses on the challenges they face when they are forced to work together. It's not just about their relationship but also about the world - building in the undertale and underfell universes. The descriptions of the settings are vivid and add to the overall charm of the story.

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.

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.

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.

The character development of Sans in this type of fanfiction is usually centered around his journey from a victim of abuse to a survivor. Initially, the abuse has left him with deep - seated insecurities and a negative view of the world. However, as he is exposed to positive influences, such as a caring friend or a new opportunity, his character begins to shift. He might start to develop new skills or interests that were suppressed due to the abuse. His relationships also change, from being guarded to more open and trusting. This development is often a slow and arduous process, but it is what makes the character so interesting in these fanfictions.

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 appeal lies in the fact that these two characters represent different aspects of the same basic concept. Fans are drawn to seeing how they can coexist or clash. Additionally, the fanfiction community around them has created a whole range of stories that range from heart - warming to action - packed, which gives readers a lot of variety to choose from.

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.