When Wagner heard Roy's group was passing through Thria on their way to the Lycian territory of Ostia with Bern's princess Guinivere, he realized they would likely stop at Castle Thria for rest. Knowing this, he assassinated Lord Orun, and planned to invite Roy's group into the castle with the excuse that Lord Orun was ill, then ambush the group and capture the princess. He would then give her to Bern to earn the country's favor.
He discussed this plan with the Thrian soldiers, who were under his command, though the plan was heard by Cath. Wagner then invited Roy and his group into the castle, and briefly left them alone in a room. While Wagner was gone, Cath approached Roy and informed him of Lord Orun's death and Wagner's plan.
Roy then made his way to the front exit of Castle Thria with his company only to be approached again by Wagner, who asked where he was going. Roy said he was leaving unless he could see Lord Orun. Wagner then decided to simply attack and kill Roy's group with his forces, not wishing to let them go. Roy's forces, knowing they were surrounded on all sides, then decided to capture Castle Thria.
He is the first actual Magic wielding Boss of The Binding Blade, which makes him rather difficult for this early chapter. In comparison with other shaman bosses in the GBA titles, he has twice the speed and has access to a throne. His high resistance makes him pretty much invulnerable to any magic attacks and any physical attackers, with their low resistance have trouble with his magic attacks. His rather high speed and his throne makes it nearly impossible to hit for many units.
Wagner is killed in the battle at Castle Thria defending the Throne of the castle.
—Wagner's death quote in The Binding Blade.