Devias is a traitor of Ostia, and thus of all of Lycia. Formerly Lieutenant Devias he was a high ranking member of the Ostian army, however upon Bern's invasion of Lyica he joined General Leygance who was forming a rebellion in Ostia. The members of the rebelling force believed Ostia (and all of Lycia) should surrender to Bern insted of fighting them.
Devias is Leygance's second in command of the rebellious forces. When Roy and company arrived in the city of Ostia (which lay just outside Castle Ostia in the territory of Ostia) Devias lead a rebel force against them with help from a handful of Bern's Wyvern Knights. Devias oversaw the defensive attack in the city from the entrance to Castle Ostia.Roy fights through the streets and kills Devias easily.
Devias is extremely loyal to General Leygance, and gave his life for him in the rebel's battle to defend Castle Ostia from Roy's forces and the Illia Mercenaries that joined in the attack. He is a somewhat fearful man, in that, he seemed somewhat afraid of fighting Roy's forces after seeing them defeat the Bern Wyvern Knights. He also knows Bors and will have a battle conversation with him if Bors is made to fight Devias.