Frisk, the fallen human, had recently fell into the Underground, and travelled around the new world they just gotten into.

Frisk walked for days, and reached Snowdin Forest. They first met Sans, a chill skeleton, and then Papyrus. The skeletons happily made room for Frisk in their home, adopting the child, in a way.

"Good morning, human!" Papyrus said with a grin as he saw Frisk waking up on the couch they've been sleeping.

"Sleep well, kiddo?" Sans smiles, ruffling Frisk's hair with care.