The story follows the player character Sigma, a man who is abducted and forced along with eight other individuals to play the Nonary Game, which puts its participants in a life-or-death situation. As the story progresses, the characters begin to unravel the secrets behind the Nonary Game, as well as its true purpose. The gameplay alternates between two types of sections: Escape sections, where the player completes puzzles in escape-the-room scenarios; and Novel sections, where the player reads the game's narrative and makes decisions that influence the story, making it branch into 24 different endings.