Following the assassination of Emperor Varis zos Galvus, Vergilia Corculum's IIIrd Imperial Legion supported Nerva yae Galvus to succeed the throne. In contrast, Quintus's Ist Imperial Legion believed that Titus yae Galvus and Nerva had orchestrated the assassination 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.
Quintus and many of his troops managed to escape tempering, taking refuge in Tertium, one of the capital's train stations. Quintus was severely injured, losing his ability to wield his weapon, but remained an effective commander, contacting the Legatus of the Xth Imperial Legion to organize an effort to reclaim the capital with the other legions. Due to his long-standing beliefs and superstitions against aether and magic, he ordered that any tempered whom his soldiers were to encounter must be put to the sword, while trying to save as many of the non-tempered citizens.
However, due to the shutdown of the ceruleum rigs, power to the capital was cut off, and Tertium began to run out of ceruleum supplies to power the aetheryte and heaters, causing many under the Ist legion's care to suffer.
Quintis is a middle-aged man with a fair complexion and swept up blond hair and a long beard, giving him the faint appearance of a lion and as with all purebred Garleans, had a third eye on his forehead. His outfit was the Law's Order of Scouting gear set, a resemblance to Final Fantasy XII's Judge Bergan.
A proud nationalist of the Garlean Empire, Quintus van Cinna believed in the vision and ideals the Empire once stood for and will defend his homeland till the very end. He is especially loyal to Emperor Varis, as it is implied that Quintus has known Varis before he took the throne and defended his claim when Nerva and the IIIrd legion attempted to usurp it. However, at the same time, Quintus is prideful, refusing to accept aid from outsiders such as the Ilsabard Contingent, instead viewing them as invaders, even when his forces are severely depleted, desperate for resources and the people under their protection are suffering. Despite his pride, Quintus is a man of honor and is somewhat reasonable, willing to hear what the Ilsabard Contingent's representatives had to say and ensuring they are not harmed. Unlike the majority of the legati the Warrior of Light has encountered, Quintus didn't underestimate them, being well aware of their reputation and skill as Eorzea's Champion. Quintus admits to being "curious" that the Warrior was not a "merciless barbarian" the Empire had tried to paint them as.
Despite being harsh and strict, Quintus is a fair leader, concerned about the lives of his men and those under their protection. However, his goal of reclaiming the capital, and thereby saving the Empire, leads to him making questionable decisions and doubt his priorities, as what salvaged resources his men had managed to gather, instead of using them to fuel the heaters for the people, he instead has them fuel what forces they had left. When he realizes that the legions he was expecting for backup aren't coming, and that they have already entered into talks with the Eorzean Alliance, he releases his men from their service, allowing them to choose their own path.
Ultimately, Quintus's central weakness is his overwhelming nationalistic pride, as he refuses any help from the Ilsabard Contingent on the principle of not wanting to 'bow down to invaders', despite his soldiers and the civilians he's supposed to protect being on the brink. When it becomes apparent that reinforcements won't come, and that the Empire has been wiped out, he's filled with such shame at the thought of bowing down that he commits suicide out of broken pride. He nonetheless honors the command to stand down when the Xth Legion gives it.