Noctis has set out on his journey to meet Lunafreya, during which he hears about the attack on Lucis' capital, Insomnia, and must fight off attacks from Niflheim magitek troops. He also remembers the Daemon attack in his childhood which left him seriously wounded: at the end of the episode, he encounters the Daemon again as part of a Niflheim attack force.

Prompto's backstory is revealed as he is tending to a wounded wild puppy found on the road. Initially an introverted and obese student at Noctis' school, his chance encounter and care for one of Lunafreya's puppies results in him being asked by her to be Noctis' friend. By the time the two were attending high school, Prompto had slimmed down and gained new confidence, though Noctis still recognized him from an earlier encounter and accepted him as a friend.

Gladiolus's origins with Noctis are shown within the frame of a monster encounter that turns into a friendly contest between Noctis and Gladiolus. Initially seeing him as a spoiled, self-centered child, Gladiolus's opinion is changed drastically when Noctis helps keep Gladiolus' sister Iris out of trouble by taking the blame for going outside the Citadel grounds with her. The two formed a close bond, which became a firm friendship by the events of XV.

The origins of Ignis' relationship with Noctis is revealed when the group stays in the town of Lestallum, and Ignis attempts to recreate a favorite dessert of Noctis'. As he begins to feel the effects of maintaining Lucis' magical Wall, Regis entrusts Ignis with caring for Noctis. While initially carefree, Noctis becomes disturbed when he sees how far Regis has declined, and has an argument with Ignis when confronted with his future as king. Eventually facing his position, Noctis and Ignis reconcile.

The episode picks up where "Before the Storm" left off, with Noctis charging at the Daemon that almost killed him. He charges at it alone, and after a fierce battle is beaten back - during the fight, he remembers everything about the first attack, including how his father only managed to drive it away. Noctis finds new resolve in these memories, and kills the Daemon with help from his companions, which causes him great emotion. The four then return to their road trip to Altissia.

A story set alongside the video game Final Fantasy XV, starring one of its main characters, Noctis, and his friends. The extended cut (released with the SteelBook Edition of Kingsglaive: Final Fantasy XV) includes the five episodes and exclusive scenes.

Similar to the way Brotherhood: Final Fantasy XV detailed the backgrounds of the four main heroes of Final Fantasy XV, Episode Ardyn – Prologue details the background of Ardyn from 2,000 years ago in Eos's history when he used to work as a healer.