A captain of the military of the Kingdom of Grangale, a major power that holds vast amounts of land in the continent's southeast. He, along with his colleague Rufus, is one of only three Slayers in the same country -- warriors strong enough to kill a Screaper alone. His manner of speech is strong-willed and somewhat rude, but that is the manifestation of his own self-confidence. He respected Lt. General Wolgainer, his direct superior, from the bottom of his heart, and didn't think pleasantly of the Peace Maintenance Brigade which forbid military movements. In fact he showed hate and spite toward them because they were the ones that fired the Admonisher on Grangale. He loyally supports his country and takes his own justice as his creed.
He is accompanied by the fairy Lottey (Lily) who loyally supports him. He is close friends with Rufus and often rescues him.
He encountered Zeonsilt's party behind the ruins of Mount Nostal when the mutant Screaper was released. He became curious about Zeonsilt's ability to weaken Screapers.
Ziekwalt was about to kill Gaerik by absorbing his life energy, but Wolgainer saved him at the cost of Wolgainer's life. Ziekwalt commented on how strong they were to endure his attack.
Gaerik gave the friendship medal to Zeonsilt, grudgingly, as Zeonsilt's party helped Grangale a number of times. Gaerik had received it from Rufus. He began to open up to the idea of cooperation in the continent and to the Peace Maintenance Brigade.
Gaerik manages the soldiers in position of the late lieutenant general although his rank stayed captain. He was present when Monopolis members came to negotiate selling Pollumine to them. He thought it would be helpful to have Pollumine reduce damage from Screapers, however he agreed with the Pothrad that it would impoverish the land's vitality too much.
In the alternate history that Shuweizer created by killing Zeonsilt, Gaerik was killed by Ziekwalt.