The only crystal left to the world lies in the Kingdom of Lucis. Upon striking a peace with the garrison state of Niflheim, Lucis rejoices in having at last brought the cold war to a close. Their celebrations, however, are premature. Under the guise of amity, Niflheim dispels the anti-armament runewall and launches a full-scale invasion of the kingdom. The peaceful lives Crown Prince Noctis and his entourage once knew are consumed by the flames of war as they struggle to mount a resistance.

Final Fantasy XV takes place on the fictional world of Eos; aside from Insomnia, the capital of Lucis, all the world is dominated by the empire of Niflheim, who seek control of the magical Crystal protected by the Lucian royal family. On the eve of peace negotiations, Niflheim attacks the capital and steals the Crystal. Noctis Lucis Caelum, heir to the Lucian throne, goes on a quest to rescue the Crystal and defeat Niflheim. He later learns his full role as the "True King", destined to use the Crystal's powers to save Eos from eternal darkness.