ImpureTale, an Undertale AU

Long ago, two races ruled over Earth, Humans and Monsters

Humans, self centered and mighty, considered themselves the purest things on the Earth, and called themselves "The Pure Ones".

The Humans gave the name "The Impure Ones" to the Monsters.

The Humans, disgusted by anything not pure, attacked the Monsters without warning.

The Monsters, unable to fight back, surrendered to the Humans.

The Humans trapped the Monsters underground with a magic spell.

However, there is a prophecy.

A child born as Impure will free their kind from underground, and the ones considered pure will be put in their right place.