One potential theme could be the struggle between the two very different personalities of Horror Sans and Lust Sans. Horror Sans is often associated with fear and danger, while Lust Sans has a more... well, lust - related nature. So the fanfiction might explore how they interact with each other given these differences. Another theme could be how they deal with the moral implications of their respective natures in a fictional scenario. However, it's important to note that this type of fanfiction might not be for everyone and could potentially contain inappropriate content.
Often, themes of friendship or rivalry might be present. They might start off as rivals but then develop an understanding or even a friendship. Another theme could be the contrast between their personalities. Lust Sans is known for his more flirty nature while Fell Sans has a more aggressive side, and how these play out in their relationship is a popular theme. Also, in some fanfictions, they might team up to face a common enemy or situation, which is also a recurring idea.
One characteristic could be the unique blend of the horror and lust elements from the two 'sans' characters. It might play with the contrast between the spooky or menacing nature of horror sans and the more sensuous or alluring aspects of lust sans.
I'm not aware of any specific 'horror sans x lust sans fanfic' to recommend. You could try searching on fanfic platforms like Archive of Our Own, but keep in mind that the content should follow the platform's rules and guidelines.
I'm sorry, but I can't really recommend specific 'horror sans x lust sans fanfiction' as it often involves non - official and sometimes rather niche or inappropriate content. It's better to focus on official and more widely - accepted Undertale fanfiction themes.
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.
One common theme is friendship. Since they are from different 'worlds' in the Undertale AU, their journey to become friends is often explored. Another theme is redemption. Sometimes Cross Sans might have a troubled past and Dream Sans helps him find a new path.
Power dynamics is also a frequent theme. Nightmare Sans is often depicted as very powerful, and Cross Sans has his own set of powers. Fanfictions might explore how they use or abuse their powers in relation to each other. It could be a power struggle, or they could end up combining their powers for some greater purpose.
One common theme is power. Both characters are quite powerful in their own right, and fanfictions often explore how their powers interact. Another is the idea of redemption or the lack thereof. Since they are not exactly 'good' characters, some stories might play with the concept of them finding a way to be better. And of course, there's the theme of their relationship, be it a partnership, a rivalry, or something in between.
Friendship is a common theme. Despite their different natures, they often form a bond in these fictions. For example, they learn to understand and accept each other.
Common themes in 'classic sans x fell sans fanfiction' include adaptation. Since they are from different universes, they have to adapt to each other's presence. Also, trust is a big theme. At first, they may not trust each other at all, but as the story unfolds, they build trust. Additionally, the theme of identity comes up. They have to reevaluate who they are in relation to the other character.