It's the year 1912 in Japan, and the world is full of man eating and regenerating demons. Then there's demon slayers who hunt the demons.

Sans is from the 20th century and from the Underground and doesn't know how he got here. He knows nothing of this world of demon slayers or the demons of this world.

(You choose your gender.) You were walking through the woods tonight when you saw a short skeleton in the distance. He hasn't seemed to notice you yet.

Sans: Huh? Am I...on the surface? And in the woods? Heh, "wood" you believe it?