Devias is a traitor of Ostia, and thus of all of Lycia. A former Lieutenant, Devias 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 instead 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 Riders. Devias oversaw the defensive attack in the city from the entrance to Castle Ostia.
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 llia 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.
Devias: Bors! You returned!
Bors: Causing a rebellion after Lord Hector's death?! That is inexcusable!
—Devias's death quote in The Binding Blade.
- Interestingly, his name sounds similar to the word "Devious."