Kris, a high school student, is a human in a world full of monsters. After arriving late to school one day, a humiliating sequence of events leads to them being locked in a supply closet with the school bully, Susie - and then the two find themselves transported to another world. There they meet Ralsei, the Prince of Darkness, who explains that the three of them are the Delta Warriors, heroes prophesized to save the world when light and dark are thrown out of balance. The trio is soon split, however, as Susie chooses to go her own way and sees violence as the solution to every conflict. With the fate of the world at stake, the rest of the team will need to find a way to reign Susie in before she makes everyone's problems worse.
Thus begins the first chapter of Deltarune, a game set in the Undertale universe. While gameplay is largely similar to its predecessor, Deltarune features an expanded battle system in which the player takes control of multiple party members. On the player's turn, they may choose to confront monsters through brute force, social interaction, magic, or even a combination of these. Enemy turns play out as bullet hell sequences in which objects representing the monsters' attacks appear and must be dodged in real time.