The world of Terresia is under assault by a "devourer", which seeks to consume its mana and leave it barren. Although the residents of the planet are unaware, this is actually a result of the actions of two entities named Widdershin and Aurora, the descenders of other worlds. As a last resort, the world's life-giving tree (the World Tree) uses the last of its power to create a defender - the player's own character. The hero, after being awakened by a strange creature named Mormo whose own world was destroyed by the same threat, learns of the danger to this world's World Tree. Upon hearing a scream, the player rushes to discover that a girl is being attacked by a soldier. After rescuing the girl, she introduces herself as Kannono, a member of an organization named Ad Libitum. This guild seeks to help the people of the world, fighting injustice and oppression. With no better leads, the player and Mormo set out to join Ad Libitum, hoping to learn more about the location of the devourer.