The player begins with the story as Kris, a human who lives with their adoptive mother Toriel, a monster. Toriel drops Kris off at school, where Kris goes toa class taught by Alphys. Kris and Susie, a monster classmate, are sent to get chalk for the blackboard. After they enter the supply closet, both of them are pulled into the "Dark World". There, they meet Ralsei, a prince of the dark, who tells them that the three of them are heroes destined to close a geyser of dark energy to restore balance to that world. However, the King has seized control of the Dark World and is determined to spread darkness.