"Warbreaker" is a fantasy novel by Brandon Sanderson set in a world where magic is derived from colors and the use of a substance called Breath. The story follows two sisters, Vivenna and Siri, who are caught in a political struggle between their kingdom of Hallandren and the neighboring Idris. The plot revolves around themes of power, sacrifice, and the nature of divinity. As the sisters navigate their roles in a complex society, they encounter various characters, including the god Lightsong and the enigmatic Vasher, who challenge their beliefs and force them to confront their destinies.