Ba'Gamnan and his siblings served as fusileers in the Dalmascan army under Prince Rasler's command. During the Garlean invasion of Dalmasca, 30 years prior to the events of Final Fantasy XIV: Stormblood, Rasler ordered Ba'Gamnan's unit to escort his twin sister, Princess Ashelia, away from the besieged Nalbina Fortress. To this end he entrusted Ba'Gamnan with an Auracite necklace to be given to Ashelia once she was safely away. Ba'Gamnan's unit ultimately failed in their duty, and both Rasler and Ashelia were killed in the invasion. Ba'Gamnan has since worn the necklace as a reminder of his failure, and seeks out more Auracite for the power to potentially undo his past mistakes.
Ba'Gamnan first appears at the end of the Royal City of Rabanastre duty, as part of the Return to Ivalice raid series. After the Warrior of Light and their party clear the Royal City, they discover both an Auracite and the missing Jenomis cen Lexentale. Ba'Gamnan and his crew fall upon the party, taking Jenomis hostage and demanding the Auracite in exchange. The Warrior of Light's party acquiesces. After releasing Jenomis and delivering a gut shot to Bwagi for a toothless joke, Ba'Gamnan steals a tome held by Jenomis. Afterwards, he, Gijuk and Bwagi flee on their airship, Auracite in hand.
Leading up to the second Return to Ivalice raid, it is discovered that Ba'Gamnan has gone missing at the Ridorana Lighthouse. Initially he is found at the base of the Lighthouse, but it becomes clear that the Auracite is manipulating him. He begins to suffer from hallucinations, seeing the Warrior of Light as Noah van Gabranth and Lina Mewrilah as Livia sas Junius, and imagining his own siblings to be Garleans. He attacks Lina, but is stopped by the Warrior of Light and collapses, reciting the pact to give his soul over to the Auracite as he dies. His body revives as a mutated monster, and flees into the tower. When the Warrior of Light reaches the peak they discover a city in the clouds along with Ba'Gamnan at the center. Upon greeting the party, he gives a speech about avenging his fallen brothers before using Auracite to transform into Yiazmat and engages the Warrior of Light.
After a long battle, the Warrior of Light emerges victorious as the True Dragon evaporates into Mist, leaving behind a necklace and a piece of Auracite. Ramza bas Lexentale attempts to pick up the necklace (believing it to be his mother's), but is struck by a magical force, rendering him unconscious. Upon returning to the Prima Vista, the cast deliberates until Ramza awakens and explains the Auracite is a "Gift from the Old Gods to guide us". Jenomis suggests that the Auracite, which contains the thoughts and feelings of its creator, seeks to return to Ivalice. Montblanc states that the necklaces (both Ba'Gamnan and Ramza's mother's) are made of cut Auracite.
Ba'Gamnan retains his original appearance from Final Fantasy XII.
Ba'Gamnan is fought in Yiazmat form as the final boss of the alliance raid The Ridorana Lighthouse.