It had started as a joke. Toriel had asked Sans to take care of Frisk for a Wednesday afternoon. Sans didn't do anything in the evening when he lived in Snowdin. And now that he lived on the surface, with all of his friends and a whole new world to discover… He still didn't do anything in the evening.
So he brought the young child to a restaurant.
The next Wednesday, Toriel had an appointment and Sans was glad to take care of Frisk again.
The third Wednesday, Frisk spontaneously asked to spend the afternoon with the short skeleton.
It became a habit. A ritual. Every Wednesday, Sans would come to pick up Frisk after school and take them somewhere fun. The skating rink, the library, the movie theater, or even just the park. Then they would go get something to eat before going back home.
One day, spotting Sans who was waiting at the doors, one of Frisk's friends yelled: "Frisk! Your lover is here!" All the kids burst into a fit of laughter and, soon, never called the skeleton something else than "Frisk's lover". Frisk didn't really care about that, if anything they thought it was funny.
But time passed and Frisk grew up. They grew up to be intelligent, strong and charismatic. And beautiful. They became a talented and respected ambassador. Very soon, the child Sans had looked after in the Underground became a very mature teenager, almost a young adult.
But neither Frisk nor Sans accepted to stop their Wednesday meetings. It was an important day, a sacred day. Their day. Frisk never stopped saying Sans was their "lover" and Sans never took offence.
And when, one Wednesday evening, Frisk realized they were kissing Sans, sitting on the low wall before their house, the human wasn't able to remember when the joke had stopped being one.
