Once Upon A Time,
Humans and Monsters lived peacefully in evergreen and fertile land. Clear, clean waters were sweet enough to drink. In the vile Danger Zone, Humans would suffer horrific deaths, while the Monsters went freely. Monsters rarely harmed the humans, but one day, a Monster killed a Human child. The Humans dismissed the killing as an accident, and forgave the Monsters. But, the killing continued, and eighty percent of all Human children had been killed. Men put up their voices and arms, saying, "We will not let the killing continue. We will drive the Monsters out." And thus, the Great War was started. The Monsters had an enormous power advantage, and began to wipe out the Humans. But one day, a beggar came to the Human leaders and spoke saying, "What if we sendthem to the Danger Zone? We can invoke an enchanted seal one them and the deadly animals, so they can never escape." But, because Fear was still in the hearts of Men, they sent Dancers to the border to keep the enchantment strong for years to come. Main Tumblr of this AU.
Sans is different from regular Sans in many ways. They act pretty much the same, but that is really all that they have in common. Underpray Sans loathes the humans, unlike UT Sans. In this AU, Sans is a Guardsman, with a permanently glowing eye that is shaped like a targeting scope. His weapon of choice is a Gaster Blaster Bow that fires blue energy arrows. He is slightly more depressed than Undertale Sans, but still tells jokes. In other interpretations of the AU, Gaster!Sans takes the place of Underpray Sans. Underpray Gaster!Sans has facial markings all over his face, and instead of using a bow, he uses a scythe-like weapon.
Frisk is a Dancer, which means they have to strengthen the enchantment. Nobody really likes them.