Well, an Undertale Undyne x OC fanfiction often explores unique relationships. It can show how the OC interacts with Undyne's strong - willed and heroic nature. Maybe the OC could be a fellow adventurer, and they bond over their love for fighting for justice in the Underground. It could also delve into how Undyne might view this new character who is different from the usual inhabitants of the game world.
There are quite a few out there. Some are available on popular fanfic websites like Archive of Our Own. You can search for them using the tags 'undertale', 'undyne', and'sans' to narrow down the results.
A third theme could be acceptance. Maybe the other characters in the Undertale universe have to accept Undyne in this new state. And Undyne herself may have to accept the changes in her body and life. This could lead to some interesting character interactions and growth within the fanfic.
I'm not sure specifically about Undyne - pregnant fanfics in Undertale. Fanfics can vary greatly in quality and content. Some might explore unique character developments or alternative storylines. However, it's important to note that not all fanfics are well - written or adhere to the original spirit of the game.
The popularity might be due to the contrast between their characters. Undyne is a fierce and determined warrior, while Sans is more laid - back. People like to explore how such different personalities could interact.
One common theme is friendship. Papyrus and Undyne are often shown building a strong bond of friendship through various adventures or just daily interactions in the Underground. Another theme is mutual respect. They both recognize each other's strengths, like Papyrus admires Undyne's fighting skills and Undyne respects Papyrus's determination.
In these fanfics, the relationship between Frisk and Undyne is often centered around mutual respect and growth. For example, they might start as adversaries but then learn to understand each other's motives. It's not about romantic or inappropriate content but more about their journey together in the game's universe.
Common themes include friendship - turned - love. They start as friends or colleagues in the Underground, and then their relationship blossoms into something more romantic. Also, there's the theme of support. For example, Undyne might support Alphys when she has problems with her scientific experiments or when she's feeling down about herself. And of course, the theme of discovery, as they discover new things about each other and about themselves through their relationship.
A good Undertale Undyne x OC fanfiction should have a well - developed OC. The OC's personality, backstory, and motives should be clear. For example, if the OC is a shy character, it should be shown how they overcome their shyness to interact with the bold Undyne. Also, it should stay true to Undyne's character traits from the game, like her loyalty and determination.
There's also a fanfiction that delves deep into their backstories. It shows how Papyrus and Undyne first met and how their initial impressions of each other changed over time. It's really interesting as it gives a lot of depth to their relationship. It also has some great dialogue that really captures their personalities.