Gly Lamprogue is the second son of the noble Lamprogue family. From a very young age, he was capable of using intermediate-level magic, a talent that made him incredibly conceited. This arrogance defined his early personality, leading him to be aggressive and dismissive toward his younger half-brother, Seika, who appeared to have no magical abilities. He also looked down upon Yifa, a slave in the Lamprogue household, and treated her with cruelty, often trying to bully and assert his will over her due to her lowly status. Gly is characterized by a deep-seated sense of entitlement and resentment, largely stemming from his belief that magical talent determines a person’s worth.

Despite his bravado and self-perceived superiority, Gly’s true nature is that of a coward. When a monster attacked the Lamprogue mansion, he was the first to flee the scene and hide, abandoning his family in a moment of genuine crisis. This act starkly contrasted with his usual bluster and cemented his role as an antagonist to Seika, who bravely subdued the creature. Even after the threat was eliminated, Gly refused to acknowledge his brother's strength, unable to reconcile his worldview that placed Seika far below him. He was eventually confronted by his father, Blaze Lamprogue, who questioned what he had truly accomplished in the past decade, forcing a change in his path.

Gly's role in the story is primarily that of a foil to the protagonist, Seika. Early on, he serves as a domestic obstacle and a bully representing the traditional magic-centric hierarchy that Seika disrupts. His primary motivation during this period is to preserve his own status and prove his dominance over Seika and those he considers inferior. Enraged that Seika and the slave Yifa were allowed to take an entrance exam for magic school—an opportunity originally meant for him—Gly challenged Seika to a duel. Unable to accept the rules set by his father, he attacked Seika on the eve of the duel and was soundly defeated, adding to his humiliation. As punishment or redirection, he was ordered to enlist in the Imperial Army.

This forced military service becomes the turning point for his character development. Although he initially resented this path, Gly found that the life of a soldier suited his combative nature. Over the course of two years, he matured significantly, both physically and mentally, honing his innate magical talents into practical combat skills to become a skilled magic warrior. He rose through the ranks to become a squad leader and was eventually scouted by the imperial princess, Fiona Urd Alegreif, to serve as a holy knight and her personal aide.

When Seika returns to the Lamprogue estate after two years, a noticeably changed Gly meets him again. While he is still prone to trading harsh words, the deep-seated animosity is gone, replaced by a grudging respect for his brother's abilities, particularly after Seika wins a martial arts tournament. He has not forgotten his past defeats and quietly desires a rematch to prove his growth, but he follows orders obediently when Fiona stops him. Their relationship evolves into a more functional, if still prickly, brotherly bond.

Regarding his abilities, Gly is noted for his use of intermediate magic from childhood, a skill he long believed guaranteed his superiority. After his enrollment in the Imperial Army, this foundation was expanded upon with rigorous combat training. He developed into an excellent magic warrior, capable of leading a squad and earning a position among the holy knights due to his proficiency in both magical and physical combat. His key relationships are with his father Blaze, who forcibly corrected his trajectory; his brother Seika, with whom he shares a competitive but ultimately reconciled bond; and his liege lady, Fiona, to whom he serves as a loyal aide.