The core concept behind Deliria is one of "ordinary people in an extraordinary world." Inspired by classical fairy tales and urban fantasy, the setting presents a multicultural world in which magic is always present but often invisible. To "twilight people" who encounter the magical realm, the world becomes a frightening yet wonderful place. Meanwhile, the immortal faeries, or aelderfolk, regard mortal humanity with a mixture of awe and terror. The accelerating pace of human imagination reverberates through both worlds, bringing changes that many aelders fear. Within the tensions of this setting, ordinary people become heroes - or villains - in their own new fairy tales.
Inspired by authors like Charles de Lint, Erik Davis and Francesca Lia Block, films like Edward ScissorHands and Practical Magic, world music and ethereal wave music, and TV shows like Buffy the Vampire Slayer, Deliria's setting emphasizes "normal people" over superheroes. As a role-playing game, it features a flexible rules system, collaborative storytelling, and a character-crafting process based on telling stories about the character. Deliria has also been noted for its vivid digital art, evocative short stories, and emphasis of "courage rather than carnage."
The core of the system is summed up as: Challenge, Prowess, Chance, Result. To resolve a Challenge, the player checks her character's Prowess. If necessary, she takes a Chance that may add to or subtract from that Prowess. Success or failure is the Result, which is then described in "story elements" - that is, narrative rather than mathematical terms.
Chances are resolved through two ten-sided dice, a deck of cards, or a computer program (sold with the main rule book).