Kris and their classmate Susie fall into an unknown place called the "Dark World" where they meet Ralsei, who informs them that they are prophesied, in the legend of Delta Rune, to be heroes that save the world.

Deltarune's full game will consist of seven chapters, each where Kris, Susie, and Ralsei either fight or act their way through Dark Worlds. Kris, being the only one who can seal the "Dark Fountain", is the party leader. They can command the other party members in battles, though some commands would seem forced to others. The SOUL, a heart-shaped object, is controlled by the player and is in Kris's body, leaving Kris's actions mostly up to the player.