The ''Episode Gladiolus'' [[downloadable content]] focuses on Gladiolus and runs parallel to the main story. During the party's travels, Prompto asks Gladiolus about a scar he acquired during a time when he took his leave of absence. Gladiolus recalls his encounter with the legendary warrior Gilgamesh. Disturbed at how easily the party is defeated in combat by Ravus, Gladiolus begins to question his ability to protect Noctis in his role as the King's Shield. Seeking the means to acquire greater power, he calls upon Cor Leonis to accompany him to the Tempering Grounds, a network of millennia-old caverns where generations of Crownsguard soldiers have sought to prove their strength against Gilgamesh, the Blademaster. Cor agrees, but warns Gladiolus that by venturing into the caverns he faces certain death and that even if he survives, he may have nothing to show for it.
As Gladiolus and Cor enter the caverns, the disembodied voice of Gilgamesh taunts them while they encounter the bodies of fallen soldiers reanimated by their souls. Cor reveals that the souls swore fealty to Gilgamesh in both life and death, and that the souls of fallen soldiers remain trapped the caverns. Gladiolus passes each of Gilgamesh 's trials and gradually learns more about Cor's previous expedition to the Tempering Grounds thirty years ago. Headstrong, reckless and arrogant, Cor confronted Gilgamesh in his inner sanctum, but fell from the cliffs into the waters below without defeating him. When he returned from the Tempering Ground he was dubbed 'The Immortal'. When Gladiolus reaches the inner sanctum, he must go on alone and face Gilgamesh in combat. Gilgamesh challenges him once again, repeating Cor 's warning that he may be risking his life for nothing. The two fight and Gladiolus emerges victorious, but not before Gilgamesh scars him. Gilgamesh reveals that there is no ultimate power, but reminds Gladiolus that he must have been a capable warrior to defeat him and so should be reassured of his ability to defend Noctis. He offers Gladiolus his favourite sword, which is revealed to have been Cor 's. Gladiolus and Cor leave the Tempering Grounds, with Gladiolus planning to reunite with the party while reflecting on the experience.