E3 completes the Trinity of Grace, the initial trilogy of the series. They are named for the three spiritual graces of Faith, Hope, and Love in Christian theology. Where E1 symbolized Hope and E2 represents Faith, E3 encompasses the dimension of Love, and this theme is prevalent throughout the story. And that's not only the aspect of romantic love, but selfless devotion and sacrifice for others in the name of Charity (one of the Seven Virtues that forms the backbone of the Sainthood, a prime tenet of the series).
Set in the realm of Chavalia, north of the great continent of Mesomia, it tells the story of a group of Rygu (extraterrestrials) who descend to the earth from the Second Firmament, an invisible plane high in the sky. The Second Firmament is an artificial mechanism created by the Rygu to keep watch over the human race. Since humans have begun to abuse the power of the Elements to advance their civilization, a dark energy has emerged from the Elemental Gates (the channels by which the forces of the Elements flow), eating away at the fabric of the Second Firmament and otherwise causing illness and suffering in the world.
The Rygu, assuming human form, must venture to the far corners of Chavalia and treat with the Elemental Guardians, who watch over the Gates, to close the Gates and halt the production of dark energy until its source can be determined and terminated. But the humans, who have come to excessively rely upon the Elements, will not let them do this so easily... Moreover, what grievous repercussions could result from closing the Gates and blocking the flow of Elemental Force?