Karion first appears at the beginning of the game, invading Niena's item shop in Xandria and stealing a medal which was given to her by her adoptive father Stein, who found it on the ruins of Kefin. Karion is confronted by Adol, warning him to not get involved before disappearing. The medal was actually the key for entering the portal leading to Kefin.
He appears again when Rizze calls him and the other lieutenants to subjugate Adol inside Dorman's mansion, to take the crystals in Adol's possession, which were needed to break the seal upon the lost city of Kefin.
Adol finally confronts Karion on the Kefin Castle's main hall, as Karion attempts to stop him from reaching the core of Kefin where the Philosopher's Stone, the source of Kefin's power, was kept, but he is ultimately defeated.
Ys Origin and Ancient Ys Vanished