Sans X Frisk.

In this story, Sans is 25, and Frisk (as girl in this book) is 21.
It had been many years since Frisk had saved all the monsters, and set them all free, and it was getting near the celebration of that, was when Frisk realized she loved Sans... and more than just a friend... And the same thing has happened to Sans.
Now, as Frisk and Sans try to figure out on how to confess their love for eachother, they are trying not to act unusual around each other.
And for all the other monsters, well, they try and bring them together, manly Papyrus, Metteton, and Asriel.