Some time prior to game's start, Oalston starts to study black magic, an ancient art which usually corrupts people's souls, but has no negative effect on him. After some time, Oalston falls ill and since then he stays in his home at Village of Trei being looked after by Dr. Cunnings. Later, the dragoons Vahn and Hans arrive with the Ancient Scale which he hands over to the doctor in order to prepare a medicine needed to heal Oalston's illness. Suddenly, a guard arrives saying that Maria went into the town's underground caves where monsters reside. Oalston quickly gets up from the bed and goes with Vahn and Hans to the caves in search of Maria, much to doctor's warning. They found Maria in the Caves attacked by a monster, but Oalston defeats it with his magic. After they return to his house, Dr. Cunnings injects the cure into Oalston. After the doctor asks why Vahn helped Oalston return to his health, the dragoon explains the situation: a man called Darius who obtained power over black magic, how it corrupts his mind, and Lord Adder's request to dispose him. Oalston suggest performing a 'purification', a process which removes black magic from a person, but requires a skilled white mage to do so. Hans suggest requesting a permition to use the Eternal Blue in order to speed up the process of finding a white mage to which both agree. At Branch Castle, Lord Adder informs them that Vicks is currently in Lenadia with the ship and it can't be used. While discussing various possibilities, Oalston mentions a town called Mystic Mysidia where mages live, and Lord Adder asks them to go there also requesting Hans to stay at the Castle if Darius were to pull something and Vahn and Oalston take Wedge from the Water Shrine with them. After getting Wedge, the three go through Trei Catacombs and Vahn and Wedge pass across Ivalice Checkpoint in their cilivian attire to not raise suspicion among Ivalician soldiers.
In Mystic Mysidia, Oalston, Vahn, and Wedge notice an argument between the town's Elder and the Ivalician generals. When the general Deckar and Eva are angry about Vera's way of interrogation, they attack her, but the party protects her. After the battle, Deckar and Eva leaves, and the Elder explains them the situation: a man clad in black armor wielding magic attacked the Citadel earlier that day and Vahn concludes that it must be Darius and they came to the town to seek a white mage who could remove the black magic from the corrupted dragoon. After discussing where the party could find Darius, Vahn theorizes that he may be after Crystals, and Elina notices the disappearance of Mysidian Flame, a symbol of Fire Crystal's well-being. The party decides to investigate the matter by going to Mount Gulgur where the Crystal resides. After passing through Mount Mysidia, Elina informs the party they will go through the abandoned town of Niflheim which lies beneath the volcano.
A year after the Great Cataclysm, Oalston goes to Lindblum and constructs a new mage academy. Oalston achieves world fame as the most skilled mage in the world and many people would come to him seeking his guidance. At the age of 72, Oalston starts to teach a 10-year-old Hautley von Muir black magic despite the boy's concern for Oalston's health in case he would hurt his teacher. Thanks to him, people start to trust black magic again.
The spells Comet and Ultima can also be learned outside of leveling. Comet will be learned when Oalston spends time in the Mage's Academy of Lindblum. Ultima can be obtained through a sidequest late in the game.
- Note: Abilities are listed horizontally as learned through leveling.