Jason is a Barbarian who is part of a trio of bandits that attacked Julie and her friends. They aimed to subdue Julie's group and steal their valuables, but Julie's friends proved too much for them. They ended up losing one of their own treasures to Julie as a peace offering.
Jason also comes from a wealthy and evil family who are working with the Souballo Empire. Jason's sister Sophia is the leader of Imperial Magical Training. Jason's father is the leader of Imperial Combat Training. Though Jason comes from an evil family, he himself is not nearly as cruel.
The woman Jason and Trevoricus were taking orders from was murdered by Umbria. Through a web of lies and bluffs, Umbria took control of the group...something Jason had little problem with, mainly due to his flaw of following the lead of whoever he deems wiser than him.
It's heavily implied that Jason had a crush on Umbria and followed her lead due to trying to please her. Through the actions of Umbria, Jason was indoctrinated into Angelo's Kids and indirectly drafted into the Souballo Empire. However, due to Umbria's cruelty and the appearance of Jane's ghost, Jason and Trevoricus kicked Umbria out of their trio.
Some time afterword, Jason and Trevoricus were summoned to the Imperial Headquarters to witness the anthem ceremony and the official launching of the airship "Brian's Big Blaster."
Since then they have risen in rank along with their powers and abilities and gained command of their own company of soldiers. The command of these soldiers proved too difficult, between their lack of command experience and Umbria's lack of concern for their welfare. They were relieved of command and tasked as a mobile strike team instead.
Their mission is to head to Silverfronds City, for Jason to meet up with his sister and to engage the enemy. To Jason's surprise (and relief) he may not have to do either with the city's latest turn of events.