A long time ago, HUMANS & MONSTERS lived together on the SURFACE, one day, a war between the two races began. After the war, HUMANS won, locking down the MONSTERS in the UNDERGROUND, they used a SPELL to create a barrier...

{10 years after Frisk fell in the Underground...}

You fall in the Underground, as you met no-one, except a skeleton with an orange hoodie.

Dustswap!Papyrus: Another Genocider, huh?

PhantomSwap!Sans: Kill them! Kill them!