Final Fantasy XV (formerly Final Fantasy Versus) is the story of a young king sworn to defend the last crystal in the world from the "hectic order" outside of his kingdom. It's a fight between ancient and modern techonology, and the struggle of one king to protect the old ways.
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.