Set in the fantasy world of Valisthea, where the people live comfortably thanks to mountains of crystal called the Mothercrystals. The world is controlled by six factions: the Grand Duchy of Rosaria, the Holy Empire of Sanbreque, the Kingdom of Waloed, the Dhalmekian Republic, the Iron Kingdom, and the Crystalline Dominion. A central part of the plot is Eikons, summoned monsters controlled by or manifesting through humans called Dominants.