Gralea is the capital of the Empire of Niflheim in Final Fantasy XV. It is located deep in the imperial heartland, and Prince Noctis's mission is to infiltrate it to take back the Crystal of Lucis. Gralea is the imperial seat of power and where the magitek laboratory Zegnautus Keep is also located, floating above the center of the city.
Nothing but daemons in the capital. Meanwhile, the Crystal's just sitting there. No one in the army signed up for this!
Prince Noctis is on a mission to recover Lucis's stolen Crystal, which he believes has been taken to the imperial capital. Daylight is vanishing and increasing numbers of daemons appear all around the world. Noctis hopes he can save Eos with the light of the Crystal, as he now has the Ring of the Lucii needed to command the Crystal's power.
Noctis and his friends ride a train driven by Biggs and Wedge into Gralea, but the train is halted by daemons. Noctis drives the Regalia into the city until it is damaged and they abandon the wrecked car on the train tracks. Noctis becomes separated from his friends and must look for a way into the imperial magitek lab, Zegnautus Keep, alone. The city streets are empty and the only inhabitants he finds are daemons.
Gralea has been ravaged by a "vanishing sickness" and its citizens have been turned into daemons. A state of emergency has been called with radio broadcasts asking everyone to stay indoors or evacuate to designated stations until it has been resolved. When Noctis makes his way to Zegnautus Keep he finds its magitek troopers have gone rogue and Emperor Aldercapt has turned into a daemon. A radio transmission Ignis Scientia and Gladiolus Amicitia can listen to on their way to reunite with Noctis implies everyone in the city has already become daemons.
According to the documents discovered in Zegnautus Keep, daemons had at first emerged in West Gralea, a majority of them confirmed escaped from military facilities. The rest were ordinary citizens who were being turned, as was later discovered. West Gralea was quarantined as the mass disappearances of people were attributed to an infectious disease connected to the daemon outbreak while other sections remained infection free. North Gralea was quarantined soon after, as the infection had manifested in five adjacent sectors, and the quarantine was expanded to encompass all areas in which daemons were found. Following the outbreaks in the north and west, daemons swept through Zegnautus Keep and control was lost over unprogrammed magitek troopers. By 28th of June more than half the Keep's researchers have turned and the city of Gralea is swarming with daemons—former citizens.
After Noctis finds the Crystal and disappears inside it, his friends escape Gralea back to Lucis, and the world is overtaken by daemons.
- Niflheim has weaponized Gargoyles to attack those who approach Gralea.