It's set in a futuristic world with cities inhabited by strange monsters called Miramon that threaten humanity and powerful citizens known as Espers. The Espers are the characters you recruit who host the powers of deities from various myths and religions, each with their own abilities and tactics which are based on their mythological inspirations.
Gameplay is based around fielding teams of up to five Espers into turn-based combat. Each Esper can use up to three Abilities, with the third one being their Ultimate, which is capable of changing the tide of battle from dealing heavy damage towards enemies, support their allies with heals and buffs, or debuffing foes with detrimental status ailments. Most Espers also have Captain Abilities, which grant a team wide buff such as increasing their damage output or strengthening their defense, though some are restricted to certain game modes. In battle, the fastest Esper usually gets to move first, unless certain buffs or debuffs are used.