Following the assassination of Emperor Varis, Vergilia's IIIrd Imperial Legion supported Nerva yae Galvus to succeed the throne. In contrast, Quintus's Ist Imperial Legion believed that Titus and Nerva had orchestrated the assassination in an attempt to claim the throne, resulting in a violent civil war between the two legions, leaving the capital city in ruins. The true masterminds behind the conflict were Fandaniel and Zenos Galvus who wanted to use the citizens' faith to summon the primal Anima, using Varis's corpse as a medium. Once summoned, the primal tempered most of the population, including Vergilia and several soldiers from both legions, into Zenos and Fandaniel's devout followers.
Once the expedition of the Grand Company of Eorzea arrived in Magna Glacies, Vergilia led troops of tempered soldiers to defend the Garlean territory. After the battle, Vergilia and the other soldiers were captured and taken away to be treated for their tempering.
Vergilia, now cured of her tempering, was later approached by the Warrior of Light and Fourchenault Leveilleur for information regarding Nerva, who had been transformed into a Blasphemy and taken residence in The Tower of Babil. She volunteered to help them kill Nerva, not wanting him to exist as a monster. She later led a party consisting of Fordola Lupis, Yugiri Mistwalker, and Lorens to recover Varis's heart, which had not been recovered after Anima's destruction and was preventing entry to the Tower of Babil. The group succeeded in their mission, allowing the Warrior of Light and their companions to breach the tower and kill Nerva.
Like most imperial legati, Vergilia wears a stylized suit of armor; her outfit is the Law's Order Healing gear, based on that of the Judge Magister Drace of Final Fantasy XII, who like Vergilia was one of the only women in their group, unlike Nael van Darnus, who hid her sex while assuming her brother's identity.
Vergilia's true disposition is at first unknown since she is tempered to serve Zenos and Fandaniel, leaving the legatus fanatic to complete the missions she is given.
Later, when she is cured of her tempering, she reveals herself to be one of the more reasonable and soft-spoken legati among the Garlean military, and she willingly aids the Ilsabard Contingent to kill the transformed Nerva before he can victimize more people.