Julius is the main antagonist in the second generation of Fire Emblem: Genealogy of the Holy War. He is the son of Arvis and Deirdre, who were deliberately brought together by Manfroy in order to ensure that they would deliver the reincarnation of Loptyr as their offspring. He is also the grandson of Victor, Cigyun, and Kurth.
Despite merely being the imperial prince, Julius is the main ruler of the Empire, as Arvis is powerless to stop his actions. This is essentially due to Azmur's dying request for Arvis to allow his son to take control of the Empire when he reached a suitable age.
Before the beginning of the Second Generation, Manfroy bestows upon Julius the tome of Loptyr, which corrupts Julius and leads him to take over the Grannvale Empire. During this time, Julius begins to destroy all traces of Naga's descendants, including killing his mother Deirdre and hunting down his twin sister Julia. Julius is also responsible for the horrific Child Hunts that take place both in the events of Genealogy of the Holy War and Thracia 776, in which children are brutally trialed and brainwashed to serve Loptyr.
Julius eventually makes his last stand in Belhalla, where alongside his twelve Deadlords, he faces off against the Liberation Army led by his half-brother Seliph. After his defeat, Loptyr dissipates into nothingness, but not before warning Seliph that he will be back so long as humans are controlled by greed.