The kingdom of Lucis, home to the sacred Crystal, is at war with the aggressive empire of Niflheim. King Regis of Lucis commands an elite force of soldiers called the Kingsglaive who wield the king's magical power. As Niflheim's overwhelming military might pushes the boundaries of Lucis, the Kingsglaive are front and center in the battle to protect their homeland. Amidst the ongoing conflict, Regis faces immense pressure to negotiate a peace treaty with Niflheim: in exchange for political marriage of his son, Prince Noctis, to Lady Lunafreya of Tenebrae, a former province of Lucis now under Niflheim's control, and the surrender of Lucis' territories, he will secure the autonomy of the capital city, Insomnia.

Nyx Ulric, a skilled member of the Kingsglaive, is drawn into this political intrigue against the backdrop of the looming armistice. With the uncertainty of motives from surrounding nations, the Kingsglaive are entrusted with the safekeeping of their kingdom's future. Following the peace treaty ceremony, Nyx discovers the duplicity and deeper, malevolent intentions of the empire. As Insomnia faces impending doom, Nyx is tasked with the protection of Lady Lunafreya, who holds the key to the kingdom's survival. Together, they navigate a web of betrayal and conflict, with the fate of Lucis hanging in the balance.