Glum begins as a timid, cowardly, and pessimistic member of the Dark Tribe, serving Dynast. He frequently expresses fear and complains, yet demonstrates loyalty to Dynast's cause. Glum possesses combat skills and knowledge from his prior service in the Mushiking royal guard before defecting to the Dark Tribe. He often participates in missions alongside other tribe members but frequently fails due to his inherent cowardice or incompetence.

Glum eventually betrays Dynast, motivated by disillusionment with Dynast's methods and goals. He defects, joining the protagonist Popo and his allies, marking a major turning point. Within Popo's group, Glum undergoes substantial development. While retaining his fearful and pessimistic core, he gradually learns courage and the value of protecting others. He forms genuine bonds of friendship, particularly with Popo, contrasting sharply with his previous relationships based on fear or obligation.

Glum develops a strong romantic interest in Maya, another member of the group. This affection becomes a recurring motivation, pushing him to act bravely despite his fears, especially when Maya's safety is involved. Protecting Maya often serves as a catalyst for overcoming his cowardice.

Throughout conflicts against Dynast and later threats, Glum evolves into a reliable, though still frequently anxious, ally. He participates in critical battles, contributing to the group's efforts despite ongoing struggles with fear. His arc concludes fully integrated as a valued friend and protector within the group, having earned respect through demonstrated loyalty and moments of bravery.