You can start by looking on fanfiction platforms like Archive of Our Own (AO3). It has a large collection of Undertale fanfictions, and you can simply search for 'undertale sans reader' in the search bar. There are usually tags and filters you can use to narrow down your results to find exactly what you're looking for.
Tumblr is also a good place to look. There are many Undertale fans on Tumblr who create and share fanfictions. Try searching for relevant tags like #undertale #sans #readerfanfiction. You might have to sift through a bit, but you're likely to find some hidden gems there.
Another option is to join Undertale - related forums or communities. People there often share and recommend good fanfictions. For example, on the Undertale subreddit, you can post a request for undertale sans x underswap papyrus fanfictions and I'm sure the community will be happy to help.
There's 'Sans and the Reader's Adventure'. This fanfiction takes the reader on a thrilling journey through the Underground along with Sans. It's full of action, mystery, and some really heart - warming moments. The way it portrays Sans' unique personality and how the reader fits into his world is really well - done.
I'm not familiar with a specific fanfiction exactly like this one. But you could look for other Undertale fanfictions with dark themes or those that involve self - sacrifice. Try searching on fanfiction platforms using keywords like 'Undertale', 'dark', 'sacrifice' and see what comes up.
Friendship is a very common theme. Sans and the reader can be portrayed as good friends who support each other through the various challenges in the Underground. Another theme could be mystery - solving, where they team up to figure out some of the secrets of the game world.
You can also try Fanfiction.net. It's an older but still popular platform for fanfictions. However, the tagging system might not be as precise as AO3. So, you might need to do a bit more sifting through the results. Another option could be Tumblr. There are often fanfic recs (recommendations) on Tumblr blogs dedicated to Undertale fanfictions, which might lead you to some great sans x reader pregnant fanfictions.
First, know the characters well. You need to understand Sans' personality - his laid - back yet perceptive nature. Start with a simple idea, like the reader meeting Sans in a specific location in the Underground. Then, build the relationship gradually. Don't rush into the romantic part right away. For example, they could start as friends who exchange jokes.
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.
Fanfiction.net is also a good place. They have a section dedicated to Transformers fanfictions. Navigate to the Transformers category and then search specifically for 'Reader Meets Bumblebee'. You might have to sift through some results, but there are often some hidden gems.
Another option is to check out dedicated Undertale fanfiction forums. These places are often filled with fans who share their own works or know where to find great 'Papyrus x Reader' stories. You might have to create an account to access all the content, but it's well worth it.
You can start by looking on popular fanfiction websites like Archive of Our Own. Use the search function and type in 'Reader x all Undertale'. Then, you can sort the results by popularity or rating. Reading reviews from other readers can also give you an idea of which ones are good.