Shortly after leaving the crown city of Insomnia, however, their car, the Regalia, breaks down, forcing Noctis to push the car to the nearest outpost along with his entourage and friends; Gladiolus Amicitia, Ignis Scientia, and Prompto Argentum. Thankfully, once they reach Hammerhead, the car is fixed up by the two mechanics working there; Cid Sophiar, an old acquaintance of King Regis; and Cindy Aurum, his spunky granddaughter.
Once the car is repaired, the four continue to a port to set off for Altissia, only to learn from a suspicious stranger that there are no ships coming. Another citizen waiting for a ship tells Noctis that a ship should come the following day, so Noctis and his crew decide to spend the night at the port's lodgings and set sail the next morning.
When Noctis wakes up the next morning, however, he learns that Insomnia has been invaded by the Niflheim Empire, the same aggressive expansionist world power that Regis sought peace with through Noctis and Luna's marriage. Noctis rushes back to the outer border of Insomnia, only to hear from the kingdom's marshal, Cor Leonis, that Insomnia has fallen and King Regis is dead.
Noctis and his friends meet with Cor, who tells the young prince that to retake Insomnia and defeat the empire, he must seek out the tombs of the past Lucian kings and gain their power. Each king that wielded the Crystal's power helped to make the royal bloodline stronger, but using the Crystal's power places a heavy toll on the king's body, causing them to age rapidly. Noctis is upset over the fact that his father lied about the true reason he was sent away from Insomnia, and over the burden that had been placed on his shoulders, but nonetheless agrees to undertake the journey and reclaim his kingdom.
Within a couple of nearby tombs, Noctis retrieves the first two souls of past Lucian kings, and with it, their weapons. As Cor departs, secure in the knowledge that Noctis will fulfill his destiny, Noctis takes solace in the fact that he doesn't have to undertake this journey alone; Gladiolus, Ignis, and Prompto are by his side.
As the group meets with Iris, however, Noctis begins to experience intense headaches, accompanied by strange visions of the Disc of Cauthess, a crater that is home to a meteor that fell to the planet and was caught by one of the Six Astrals of Eos, Titan.
After retrieving another royal weapon from a nearby tomb, the mysterious stranger that Noctis met earlier, introducing himself as "Ardyn". He offers to escort Noctis and his friends to the Disc to get to the bottom of his migraines. While Noctis and his friends don't trust Ardyn, they decide to follow his lead nonetheless.
As Titan begins to fade away, Ardyn arrives in an airship to ferry the prince and his friends to safety, revealing himself to be Ardyn Izunia, Imperial Chancellor of Niflheim. The Archaean vanishes, and the world worries as to what this could mean...
Buoyed by the knowledge that Luna is lending the support of the gods to his cause, Noctis sets out to complete a trial by Ramuh to earn his favor. After completing Ramuh's test, he learns from Cindy that the Regalia is being kept at an imperial base. Noctis and his friends infiltrate the base at night to retake the car before the Empire and use the break in the weather to take it away. Before they can leave, however, they are intercepted by Ravus, Luna's elder brother and a former prince of Tenebrae before it was annexed by the empire. Now the high commander of Niflheim's military, he engages Noctis and his friends, but is called off by Ardyn, who grants Noctis safe passage out of the base.
As the team ponder Ardyn's motives and the source of Ravus's superhuman strength, they learn from Iris upon returning to Lestallum that Jared had been murdered by Imperial troopers when they scoured the city for Noctis. With Lestallum no longer safe, Iris and young Talcott must seek shelter elsewhere...
The following day, the group arrive at Camp Caem, where Iris takes up shelter in an old house. Cid and Cindy are also on the scene; King Regis's boat is being kept in a port at the camp, and they are hard at work in completing repairs and making it seaworthy.
Upon arriving at the Vesperpool, Noctis and his two friends run into Ardyn once more. Ardyn escorts Noctis and his crew to the entrance to ruins that house the Mythril and gives them the aid of Aranea, the commodore they had fought earlier. Aranea, in truth, was a mercenary before entering Niflheim's employ; when not fighting Noctis and his friends, she proves to be friendly and affable. She also has grown suspicious of the Empire's true motives; with the Crystal gone from the crown city, the daemons that it had kept at bay have grown stronger when they emerge at night, and the Empire had been hunting them down in order to make new Magitek Troopers. She considers leaving the Empire and becoming a mercenary once more.
After retrieving the mythril, Aranea takes her leave, wishing Noctis well and advising him to walk his own path.
With the ship finally repaired, Noctis can finally depart for Altissia.
As Luna summons Leviathan and asks for her aid, Noctis fights off Niflheim soldiers to prevent them from interfering. The only way Leviathan will entreat her aid to Noctis's cause is if he proves himself worthy, so Noctis engages the goddess in battle. As Noctis fights a desperate battle against the Hydraean, Ardyn appears once more and stabs Luna. With her strength fading, Luna uses her power to invoke the souls of past Lucian kings, giving Noctis the power he needs to fell Leviathan with the aid of Titan.
Noctis loses consciousness afterwards and has a dream of Luna saying her farewells to him before passing the Ring of the Lucii onto him. When Noctis awakens, he learns from Ignis, who had been blinded during the fighting, that Luna is dead. She had left the Ring to him before passing. Noctis breaks down into tears as the love of his life is no longer of this world...
The train makes a stop at a mining town, which they learn houses another tomb. They make their way towards the tomb, having to take their time to account for Ignis's blindness. After retrieving the royal arm, Ignis reaches his limit with Noctis and Gladiolus, telling Noctis that a king cannot lead by remaining still, and telling Gladiolus that Noctis will take his place when he is ready. The gulf between the friends mended and their resolve renewed, they press on to Gralea.
As they travel to the Imperial capital, they begin to note that the nights are growing longer: with Lunafreya's death, daylight is growing increasingly rare, and the daemons are becoming stronger. If there is any hope for halting the coming darkness, it is with the Crystal...
Noctis meets with Aranea once more, who has left the Empire and is now aiding Tenebrae in humanitarian efforts. She offers her two most trusted soldiers, Biggs and Wedge, to help drive the train to Gralea so that civilian lives would not be jeopardized.
The group resume their journey to Gralea, along the way encounter the cadaver of one of the Astrals; Shiva, the Glacian. Shiva's death had caused a violent snowstorm to envelop the surrounding area, halting the train. Ardyn appears to taunt Noctis, but is silenced by Gentiana, an aid to the late Lunafreya and, in truth, the vessel of the goddess Shiva. Shiva tells him of the War of the Gods before giving her blessing to Noctis, and warns him that Ardyn is immortal. After conveying Luna's feelings of love for Noctis, she departs, and Noctis resumes his journey to Gralea in the hopes of finding the Crystal and Prompto...
Upon arriving at Zegnautus Keep, the military base where the Crystal is housed, Noctis becomes separated from Gladiolus and Ignis. As Noctis finally finds the strength to wear the Ring of the Lucii, he fights his way through the base, along the way finding the body of Ravus and the sword of his father that Ravus had taken. Letters found around his body revealed that, in spite of his reservations about Noctis, he had always been loyal to Lunafreya and aided her to the best of his ability.
Meanwhile, Ignis and Gladiolus encounter Ardyn, who shows them security footage of Ravus's last moments: Ravus had confronted the Emperor, telling him that Noctis is the one true king of the land. In response, the Emperor summons daemons to deal with Ravus before Ardyn, disguises as Noctis, stabs him to death.
Eventually, the three reunite and find Prompto, who had been kept in a laboratory by Ardyn. Prompto reveals that he was actually created by the Empire to be made into a Magitek Trooper, a barcode branded into his wrist serving as proof. He is worried about what his friends would think, but thankfully, Noctis and the others don't care where he comes from; as far as they're concerned, he is still Prompto.
As they proceed further into the base, they encounter a daemon-possessed Ravus who begs Noctis to end his suffering. After defeating Ravus, daemons descend on the area, forcing Noctis to leave his friends to fend them off as he finally finds the Crystal.
Noctis approaches the Crystal and reaches out to it, asking for it to grant him the power to banish the darkness. To his horror, however, the Crystal begins to absorb him. Ardyn appears to twist the knife in Noctis once more, revealing in the moments before he is completely pulled into the crystal that his real name is Ardyn Lucis Caelum: Ardyn was Noctis's ancestor, but he was denied the right to become the One True King due to his affinity with the darkness and daemons. His soul had become corrupted due to his work as a healer exposing him to the Starscourge, a plague which was responsible for the creation of daemons and the darkness blanketing the world. Scorned by the Crystal and unwelcome in the afterlife, Ardyn had roamed the world for eons, vowing to bring about an age of darkness and ruin. Believing there would be no satisfaction in killing Noctis as he is, he invites him to come back and fight him again once he had become the One True King.
Within the Crystal, Noctis is approached by one of the Astrals; Bahamut, the Draconian. Bahamut explains that Ardyn is the source of the darkness threatening the world and that if he is to restore the light to the world, Ardyn must be defeated. The power of the One True King would be Noctis's once the power of his forebearers was passed onto the Ring of the Lucii, but to dispel the darkness and deliver the world from ruin, Noctis must sacrifice his own life.
At Hammerhead, Noctis finally reunites with Gladiolus, Ignis, and Prompto. Together, they resolve to make their way to Insomnia, defeat Ardyn, and end the age of darkness.
After one last meal by a campfire, the four make their way to Insomnia. Together, they fight their way past the daemonic hordes and find a base of remnant Kingsglaive soldiers in the subways beneath the city led by Cor. After reuniting with their old friend, Noctis and his friends continue on, only to find Ardyn waiting for them. Taunting the king, Ardyn erects a barrier around the Citadel where the Crystal and the throne lie: it is the same Wall that had protected Insomnia before Niflheim's invasion.
As Noctis and company continue toward the Citadel, they encounter a powerful daemon known as Cerberus. The hellish hound proves to be a challenging foe, but Cor arrives and helps even the odds. As Cerberus falls, it fires one last blast of flame that badly wounds Cor. The marshal says his farewells to Noctis before leaving.
Even with Cerberus gone, the wall proves to be an immutable obstacle, and daemon hoards are converging on Noctis and his friends. As all hope seems lost, Lunafreya's spirit appears and calls upon the gods that entered into the Covenant with Noctis; Ramuh, Shiva, Leviathan, Titan, and Bahamut all appear to destroy the daemons gathering on Noctis and break down the wall, opening the Citadel for Noctis.
Beyond the gates leading to the Citadel, Noctis and his retinue encounter Ifrit, the Infernian; one of the Astrals and a god who holds humanity in disdain. Together, along with Bahamut and Shiva, Noctis and his friends fell Ifrit. In the Citadel, Ardyn presents more obstacles between Noctis and the throne: three of the Rulers of Yore, revived by Ardyn and corrupted by the Starscourge. With the help of his friends, Noctis defeats these old kings of Lucis, with the third and final Ruler beseeching Noctis to defeat his "brother", Ardyn.
Within the throne room of the Royal Citadel, Noctis finds Ardyn. Ardyn incapacitates Noctis's friends, explaining that theirs would be a battle between kings. Finally, the two princes of Lucis fight, and in the duel that ensues, Noctis defeats Ardyn, who promises to see Noctis "on the other side".
Noctis returns to the throne room and, having made peace with himself and come to terms with his duty, calls upon the kings of old. As the spirit of his father, King Regis, watches, the souls of the previous kings attack Noctis. Regis lands the final blow upon Noctis, bringing his soul into the Ring of the Lucii. With the power of kings now finally united, Noctis confronts Ardyn in limbo and destroys his corrupted soul, killing him once and for all. As Noctis's own soul dissolves into light, the Ring of the Lucii disintegrates.
The darkness is dispelled. The sun rises over the land once more, the daemons are destroyed by its radiant light, and peace returns to the planet once more as Noctis and Lunafreya finally reunite in the hereafter...
At the Tempering Grounds where Gilgamesh resides, Gladiolus attempts to fight the Blademaster, but is soundly rebuffed. Throughout the grounds, Gladiolus engages in a series of trials to test his strength, succeeding each time before fighting Gilgamesh once more. The battle proves to be more of an equal measure of strength this time, with Gilgamesh, who was missing his left arm, conjuring an aetherial replacement arm to even the odds. In the end, even though he is scarred across his forehead, Gladiolus emerges victorious. Gilgamesh, learning that Gladiolus's one feat was falling short of his duty to protect the king, deems Gladiolus worthy to be the King's Shield and gives him a parting gift: the Genji Blade, the katana he took from Cor during their battle long ago, and the selfsame weapon that took his arm.
When he comes to, Prompto finds himself in a strange room. Ardyn is nearby, claiming Prompto was back home while giving him his pistol and urging him to meet his "father". Troubled by Ardyn's words and the fact that doors in this building open when has the strange barcode brand on his wrist read by the locks, Prompto fights his way through the facility, one used by the empire to manufacture magitek troopers.
Eventually, Prompto finds Verstael Besithia, the foremost scientist in Niflheim's military, talking with Ardyn. Besithia, who is turning into a daemon, reveals that the magitek troopers are created from clones, all grown from his genes, who are transformed into daemons by their exposure to the Starscourge before being converted into magitek cyborgs. Worst of all, Prompto was one of his clones, who had been taken from a facility and brought to Lucis to be raised as a normal child. Now seeking to make himself even stronger than divinity by making himself a daemon and merging his soul with magitek, he lurches towards Prompto. Prompto, scared and in denial, shoots Besithia in the face, killing him.
As Ardyn taunts him, Aranea appears and helps Prompto escape by snowmobile. When the two set up camp, Aranea urges Prompto to return to his friends, having met with them in Tenebrae and learning that they were worried for their missing companion. Prompto is hesitant to return, troubled that the truth of his origin as a Niflheim clone would cause his friends to reject him. Aranea, annoyed with Prompto's self-pity, tells him that he should focus less on what others want and more on what he wants.
The following day, Prompto walks out into the fields and finds several downed magitek troopers. One of them, wounded, reaches out to him. Prompto, relating to the trooper and feeling pity for it, kills it out of mercy. He then begins to have a waking nightmare of Noctis attacking him, seeing himself as a magitek trooper, and flees into the forest until he finds Pryna, Lunafreya's pet dog. He thinks back to his childhood, living in secret in Lucis and hiding the barcode brand on his wrist, scared of rejection and never having friends. That was when Pryna delivered a message from Lunafreya asking him to befriend Noctis. He had long wondered why she would make such a request of him: after all, he was a fake person. How could he ever be friends with the Crown Prince?
Pryna guides Prompto to a vision of his younger self; a small, chubby, bespectacled boy. Seeing himself as he was, he takes Aranea's words to heart, reuniting with her as she prepares to return to the magitek facility and proclaiming his intent to help her, then reunite with his friends: even though he still worried what his friends would think of him, it is his desire to meet them again and face what comes.
Together, Prompto and Aranea storm the facility to destroy "Immortalis", the top-secret magitek weapon that Besithia had fused his soul with. Immortalis activates, a massive magitek monstrosity guided by Besithia's soul, and gives chase after Prompto and Aranea. Prompto, however, uses a machine gun mounted on the back of a snowmobile Aranea drives to fight back, eventually destroying Immortalis and finishing off his "father" for good and all. With the daemons of his past put to rest, Prompto parts ways with Aranea and makes his way to Gralea, where the Crystal is being kept and where Noctis and company would surely be headed next...
Along the way, Ardyn captures Prompto and imprisons him in Zegnautus Keep. Eventually, Noctis, Gladiolus, and Ignis find and free him.
As the group take shelter in a rest area, Noctis apologizes to Prompto for having fallen for Ardyn's trickery and attacking him. He then vows to break down the borders between Lucis and Niflheim as king to help bring about lasting peace in the world, with Prompto noting that Noctis is finally coming into his own as king.
Now, the city of Altissia burns as Niflheim invades it in an attempt to fight of Titan, having been summoned to aid Noctis in forging a covenant with Leviathan. Separated from Gladiolus and Prompto, Ignis makes his way to the Altar of the Tidemother, driving off Niflheim's soldiers along the way. As he tries to make his final approach to Noctis, he is pursued by a Niflheim general piloting a custom-made magitek armor. In the pitched fight that follows, Ignis disables the armor.
As the general emerges from the armor, he is suddenly stabbed by Ravus. Although Ravus still holds Noctis in disdain, the threat that the empire poses to his sister Lunafreya gives him and Ignis a common enemy, the two fighting off magitek troopers and armors together.
Upon reaching the altar, Ignis finds Pryna, Lunafreya's messenger dog, badly wounded. Suddenly, he receives a vision of the future to come, of Noctis banishing the darkness from the world, but offering his life in sacrifice to deliver the world from ruin. When he comes to, he and Ravus find Noctis and Lunafreya. Noctis is unconscious, but alive. Sadly, however, Lunafreya lies dead beside him.
Consumed by grief and rage, Ravus draws his sword to kill Noctis. Ignis stops him, the two fighting a fierce battle until Ignis helps Ravus see reason: Lunafreya willingly laid down her life so that Noctis could save the world, and to kill Noctis would mean forsaking her sacrifice. Ravus, still grieving, cradles his sister's body as her spirit smiles down on them nearby.
There is little time to catch their breath, however, as Gladiolus arrives. Ignis notices something amiss with Prompto absent as Gladiolus suddenly attacks Ravus. Ravus deflects the attack, recognizing "Gladiolus" as Ardyn in disguise. With Noctis still unconscious and Ignis detained by magitek troopers, Ravus fights to defend them, but is rebuffed by Ardyn, who turns to Ignis and offers a deal; he would spare Ignis's life in exchange for abandoning Noctis to his fate...
Ignis, however, adamantly refuses. He shoves off the magitek troopers and takes up the Ring of the Lucii, which was in Noctis's hand until Ardyn's interference caused it to slip from grasp. Reaffirming his vow to protect Noctis and willing to sacrifice his life in to ensure his friend would not have to lay down his, Ignis places the Ring on his finger. His eyes are enveloped by violet flames that permanently rob him of his sight, but with the power of the Lucian kings of yore, Ignis is able to fight Ardyn on equal footing and drive him away.
With the crisis averted, Ignis, his face now scarred and his glasses now tinted to hide his blindness, asks Noctis if perhaps they should give up on their journey and return home, reasoning that they already lost too much. Noctis refuses, claiming that it is precisely because of everything they lost that they must push on. Ignis remains troubled by the vision he had of Noctis's fate, but nonetheless agrees to aid him until the bitter end...
Ten years later, before they make their way to Insomnia, Noctis and Ignis confer in private. Noctis confides that he probably couldn't have come this far without the aid of his friends, and personally thanks Ignis for sticking by him. Ignis flashes back to when he first met Noctis, when the two shook hands as the young prince beamed at him. As he had back then, Ignis extends his hand to Noctis. Noctis clasps Ignis's hand in his, and the two smile warmly at each other, tears of joy welling in Ignis's sightless eyes...
Eventually, Ardyn was found by soldiers of the Niflheim empire, led by the scientist Vestrael Besithia. As the soldiers extracted Ardyn, Crownsguards descend on the island, killing the soldiers and attacking a weak and weary Ardyn. The injuries from the Crownsguards' attacks cause him to once more lose control of his daemons, lashing out and descending on one. To Ardyn's surprise, he didn't extract any daemons from his victim: instead, he daemonified them, and in so doing, took their memories into his own mind before losing consciousness.
Some time later, Ardyn awakens in an Imperial research facility, where Besithia explains that Ardyn, given the tentative surname of "Izunia", was a scientific marvel: neither a human nor a daemon, but a combination of both. This duality to Ardyn's very nature made him far stronger and more resilient than humans, but also allowed him to move about in broad daylight with little ill effect. His ability to absorb the memories of those he daemonifies is also of keen interest to Besithia. After explaining that the Lucian kingdom continued to thrive in the thousands of years since he was imprisoned, Besithia shows Ardyn the captured body of one of the Astrals: Ifrit, the Infernian, whom Besithia wants Ardyn to daemonify, absorbing the god's arcane memories in so doing.
Crownsguards break into the facility to destroy Adagium, and in the fighting, Ifrit awakens. As the Infernian picks him up, Ardyn beseeches Ifrit to grant him the power to destroy the Lucian kingdom. With his powers, he corrupts the Infernian, bending the god's will to his own as he is haunted by visions of a Starscourge-stricken Aera and a taunting Somnus forcing him to kill her while she begged forgiveness for denying the Crystal's will and telling Somnus of his ascension: an act that led to her death and Ardyn's captivity.
Scorned by the gods and his mind twisted by hatred, Ardyn vows to lay the kingdom of Lucis to waste and end the Caelum bloodline.
Over the next several years, Ardyn helps the Niflheim empire conquer most of the known world, aiding in the creation of magitek infantry units and forcing Lucis to pull its defenses back to its capital of Insomnia...
Then, one day, Ardyn arrives in Insomnia to lay siege to the city during Founder's Day, a holiday celebrating Somnus. With the corrupted Ifrit at his side, Ardyn helps Niflheim destroy several amplification devices that bolstered the city's protective Wall so Niflheim could invade. At each amplifier, a Guardian bearing the shape and memories of one of the Kings of Yore stood guard, giving Ardyn an idea: if he could force the king to summon the Old Wall, he could settle the score with Somnus. Thus, against Besithia's orders, Ardyn goes to confront the Lucian king: Regis Lucis Caelum.
Ardyn fights Regis and manages to defeat him, knocking him unconscious. Moments after, the Ring of the Lucii summons the spirit of the first king, Somnus. Somnus explains to Ardyn that the corruption in his soul made him unfit to rule, but he had always regretted having betrayed him. Ardyn, however, throws Somnus's pleas for understanding back in his face as he defeats him.
Finally, Ardyn goes to kill Regis, only to be stopped at the behest of another Astral: the Draconian, Bahamut, who pulls Ardyn into limbo to explain his place in the world. According to Bahamut, Ardyn's purpose is to be the one who plunges Eos into darkness, so that the True King would confront him and kill him. In so doing, the True King would also die, thus spelling the end of the Lucian bloodline. To resist the will of the Astrals would mean subjecting himself to eternal torment.
Although the gods would have Ardyn serve as the world's sacrificial lamb, he has no interest in obeying their will, not after having been scorned by them and the ones he loved. Thus, Ardyn makes a solemn vow: to engulf the world in eternal darkness, and when the True King came, to kill him...