One main theme is identity. Since it's an underswap, their identities are different from the original, and exploring how they adapt to these new roles is a big part. For example, if Papyrus is more like the original Sans in some aspects, how does he deal with that change.
Common themes include loyalty. They are extremely loyal to each other in most fanfics. Another one is the theme of overcoming challenges. Whether it's dealing with other characters or facing difficulties in their world, they work together to overcome them. There's also the theme of fun and humor. Their interactions are often filled with jokes and light - hearted moments, which makes the fanfics enjoyable to read.
A common theme is the exploration of differences. Since they are from different universes, their personalities and ways of life are different. Fanfics often focus on how they deal with these differences.
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.
A third common theme is self - discovery. Both Papyrus and Sans might learn new things about themselves as they interact with each other and face various situations. This can be really interesting as it shows their growth as characters. For instance, Papyrus might discover a new side of his personality when he has to protect Sans in a dangerous situation.
The plot matters a great deal. It could be about their adventures in the Underswap world, or it could be a more emotional story about how they deal with the changes in their relationship due to the swap. A good plot keeps the reader engaged, whether it's full of action, humor, or heart - felt moments. For instance, a plot where they have to work together to save their swapped world from a threat would be exciting.
One great idea for a fanfiction could be a story where Underswap Sans and Underswap Papyrus go on an adventure in the Underground. Maybe they encounter a strange new monster that no one has ever seen before. They have to use their unique abilities to figure out how to deal with this new threat.
One common theme is the exploration of differences. Underfell sans and underswap papyrus are from different universes with distinct personalities. Fanfictions often focus on how they deal with these differences, like underfell sans's more aggressive nature compared to underswap papyrus's more positive and energetic self.
The writing style is crucial. A good fanfic will have smooth and engaging prose. It won't be full of grammar and spelling mistakes. For this pairing specifically, the interactions between the two should be believable. They come from different 'universes' within the Undertale multiverse, so how they react to each other's differences and similarities can make or break the story. Also, a bit of humor or emotional depth can really enhance the fanfic.
A plotline could be that they discover a hidden part of the Underground. This new area could have different rules and strange creatures. They have to adapt quickly to survive and also figure out how this new place relates to the rest of the Underground.
A great Underswap Sans x Papyrus fanfiction might be the one that delves into their backstory. It could explore how their relationship developed from when they were younger. Maybe there was a time when they had a big fight but then learned to understand each other better. This kind of story can be really heartwarming as it shows their growth and the strength of their brotherly love.