Garm is the Incarnate form of a former soldier named Roy, who fought alongside Hank Henriette in the civil war that serves as the backstory for the series. The process to become an Incarnate was born from painful experimentation on human soldiers, transforming them into powerful but monstrous beings. In his previous human life, Roy was an infantry soldier known for charging enemy bases, and he took great pride in the trust his commanding officer, Hank, placed in him as they fought side by side. This loyalty to Hank is a defining trait of his character, as he valued their bond as canines in the same unit.

As the story progresses, Garm becomes a follower of Cain Madhouse, an Incarnate who has rejected humanity and leads others like him in the Free Nation of New Patria. Despite this change in allegiance, Garm retains a deep-seated respect for Hank, his former commander. He is shown to be proud of the oath they made in the past and does not see himself or his fellow Incarnates as mere beasts, but as warriors with will and pride. His motivations are driven by a desire to have Hank return to lead them, and he views Hank's resistance to his own beastly nature as an insult. In the absence of Hank, he has turned his loyalty to Cain, who is willing to give direction to the scattered Incarnates.

Garm serves as a direct antagonist to Hank, representing a personal and painful confrontation with his past. Their shared history as comrades makes their battle a tragic one, as Hank is forced to kill someone who was once a friend and subordinate. The conflict is a central part of the narrative, highlighting Hank's mission to hunt down the very soldiers he once led. Garm's role in the story forces Hank to confront his own crumbling psyche and the burden of his oath. He urges Hank to give up his human form entirely, wishing to fight him as true beasts, which underscores the tragic loss of humanity that defines the Incarnates' existence. One review also notes that Garm is implied to have had a pre-existing crush on the protagonist Schaal, adding another layer to his character.

The relationship between Garm and Hank is the most significant in his narrative. They are former allies whose bond has been shattered by the war's end and the subsequent corruption of the Incarnates. Their confrontation is depicted as a battle between two canine Incarnates, a white wolf and a black wolf, representing their opposing paths. Garm's development is shown through flashbacks to his human life, illustrating the proud soldier he once was, and his eventual fate at Hank's hands, where he is killed after a fierce battle. In his final moments, there is a brief reminiscence between the two former friends before Hank delivers the fatal blow, allowing for a moment of tragic closure.

In terms of abilities, Garm is an Incarnate whose form resembles a werewolf. Unlike some Incarnates who can revert to a human shape, Garm has seemingly lost that ability, remaining in his beastly form, and he possesses superior strength and speed. While his abilities may appear straightforward compared to other Incarnates with more fantastical powers, his swiftness and sharp claws are more than sufficient to deal fatal blows to humans. He relies on his innate muscular strength and speed to attack his prey and is capable of eliminating multiple trained soldiers from the Coup de Grace squad in a single encounter. As a canine-type Incarnate, he also instinctively gathers information about his surroundings using his keen senses of hearing and smell. His power is such that he is a formidable opponent even for Hank, pushing his former commander to his limits.