Donny is a notable supporting character and a core member of the main traveling party, often referred to as the Percival Platoon. He is a young man with a lanky build and long red hair, which he typically keeps tied back, and he is often seen wearing a tunic and a hooded cloak. His youthful appearance is marked by a perpetually worried or surprised expression, which complements his initial demeanor. As a human with magical abilities, he originates from the kingdom of Liones and has a significant personal connection to its Holy Knights, being the nephew of the Great Holy Knight Howzer.

Donny begins the story as a member of the Katz Street Troupe, a wandering performance group where he uses his magic for levitation tricks to earn money. Before this, he was an apprentice Holy Knight training under his uncle. However, he abandoned his training due to a deep-seated fear of death and a reluctance to risk his life for strangers, a decision influenced by his dying mother asking him to live on her behalf. This background establishes his initial character: a self-proclaimed coward who is cynical, weary, and primarily motivated by self-preservation and financial gain. When he first meets the protagonist, Percival, Donny attempts to rob him using his telekinetic powers, revealing his initial unscrupulous nature.

Despite his rough and cowardly exterior, Donny possesses a strong moral compass that he initially tries to suppress. His core motivation shifts dramatically after he is inadvertently swept into Percival's journey by the magical teleportation of the talking fox, Sin. Forced to travel with the optimistic and fearless Percival, Donny finds himself repeatedly stepping into danger to protect his new friends. He is driven by a growing sense of loyalty and a desire to live up to the ideal of a Holy Knight that he once abandoned. While he frequently vocalizes a desire to flee from powerful enemies and complains about their perilous situation, he consistently cannot bring himself to abandon innocent people or his companions in need.

Within the group dynamics, Donny serves as a grounding presence. He is often the voice of reason and caution, acting as a foil to Percival's naive heroism and Anne's hot-headed impulsiveness. His relationship with his uncle, Howzer, is a key part of his backstory, driving his initial sense of shame and his eventual goal to become a worthy Holy Knight to make his family proud. He shares a sibling-like, bickering dynamic with Anghalhad (Anne), frequently clashing with her but ultimately working together seamlessly as trusted teammates. His perspective on Percival evolves from seeing him as a naive mark to a genuine friend whose unwavering hope inspires Donny to be braver than he believes he can be.

Throughout the narrative, Donny undergoes significant character development, transforming from a selfish dropout into a courageous and empathetic hero. His growth is marked by a Took a Level in Badass arc, where he not only gains confidence but also masters his magical abilities. He progresses from using his power only for mundane tasks like catching fish or petty theft to wielding it effectively in combat. A turning point in his development is his decision to return to a hopeless battle against the fearsome Holy Knight Ironside, despite having initially run away, proving that he has overcome his defining weakness. After a two-year timeskip, this development is shown physically as he gains a more muscular build, further resembling his uncle and reflecting his maturation into a capable fighter.

Donnys notable abilities center on his magical power, Telekinesis. Initially, he believed this power merely allowed him to levitate small objects and people. Under the guidance of Sin, he learns to use it with far greater precision and force, eventually becoming capable of manipulating objects and hurling powerful opponents as if they were weightless. In addition to his magic, he is a skilled knife fighter, having received extensive training in bladed weapons from his uncle Howzer. He can use his dagger in close-quarters combat to launch rapid attacks. A notable team technique he participates in with Percival, Nasiens, and Anghalhad is the Quartet Attack Slash Squall, where the four synchronize their swordplay for a unified offensive. His fighting style is pragmatic, often combining his telekinesis to control the battlefield while using his agility and knife skills to handle immediate threats.