One idea could be a story where Fell Sans and Fell Toriel form an unlikely alliance. Maybe they start by just having chance encounters in the Underground, and over time, they realize they share a common goal, like trying to bring some sense of order to the chaotic Underfell world. This could involve them working together to deal with unruly monsters and gradually growing to respect each other.
To write a great Undertale Underfell Sans x Fell Toriel fanfiction, you need to research the Underfell universe thoroughly. Know the rules, the power dynamics, and the overall atmosphere. When it comes to their relationship, start with small moments. Maybe Fell Sans brings Fell Toriel a small gift, like a flower from the dangerous parts of the Underground. This simple act can start to break the ice between them. As for the writing style, use vivid descriptions to bring the Underfell setting to life. Describe the dark corridors and the menacing monsters in the background as their relationship unfolds.
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.
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.