There are fanfics that focus on the more emotional side of their relationship. For example, a fanfic might explore how Underswap Sans helps Frisk deal with the trauma of their previous Underground experiences. He could use his unique charm and understanding to comfort Frisk, which makes for a really heart - warming read.
Another theme is discovery. Since Frisk is new to the Underswap world, they discover new things about it with Sans. Sans, in turn, discovers new aspects of himself through his interactions with Frisk. This mutual discovery is a big part of many stories.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfics from various fandoms, including Underswap. Just search for 'Underswap Sans x Frisk' in the search bar, and you'll likely find many options.
One common theme is adventure. Sans and Frisk often go on various adventures in the Underswap world. Another theme is friendship, showing how their relationship develops over time.
One popular Underswap Sans x Frisk fanfiction is 'A Different Tale'. It explores a unique relationship between them where they face various challenges in the Underground together. The story has some really interesting character interactions and a well - paced plot.
You can try searching on Archive of Our Own (AO3). It has a large collection of fanfictions, including those related to sans x frisk in the Underswap universe. Another option is Fanfiction.net, which also has a wide range of fan - made stories.
To write a great Error Sans x UnderSwap Sans fanfic, start with a strong concept. Maybe it's a story about how UnderSwap Sans tries to 'fix' Error Sans in some way. Research the existing fan works and the official Undertale lore to get inspiration. When it comes to the writing itself, build up the relationship between the two characters gradually. Show how they initially react to each other, and then how their relationship evolves over time. Use vivid descriptions for their actions and the settings around them. For example, describe how Error Sans' glitches affect the environment they are in, and how UnderSwap Sans' positive energy can sometimes counteract that. Also, make sure the pacing of the story is right, not too slow or too fast.
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.
There's also 'Swap Brothers' Bond'. This fanfic delves deep into the brotherly bond between Sans and Papyrus in the Underswap setting. It shows their daily adventures and how they support each other. The author does a great job of capturing the essence of their swapped selves, and it's full of humorous and touching scenes.