Grimm is a sorcerer whose entire form is wrapped in white feather bandages possessing healing properties and protective capabilities for himself and others. His bandaged face features red glasses over each eye and pointed teeth drawn across the mouth area. He typically wears a black pointed hat adorned with a feather, a black cloak, black pants, white shoes, and white gloves marked with a single drawn eye. A belt secures storage scrolls holding his weapons.

He consistently speaks in the third person, a mechanism for self-regulation and emotional control, though unconventional and socially disruptive. His demeanor remains calm and polite, yet fierce battle instincts surface during confrontations with nemeses or fellow sorcerers. Grimm harbors an intense fear of blood, manifesting as paranoid precautions against his blood contacting others or the environment; he stores it with extreme security. Despite high self-awareness, his accelerated information processing and actions frequently cause misunderstandings.

Grimm wields diverse magical abilities focused on Fantasia manipulation, emitting dark blue energy. His spells often bear musical names: **Procella** fires a beam of blue flame-like energy; **Veneticium Revelare** releases slashing waves through spinning or enables distant vision; **Caeca Nube** deploys detonatable Fantasia balls creating smokescreens; **Nube** generates explosions that birth shadow figures. His feather bandages heal and can absorb entities, sealing them within before later release. He employs the large sword **Kannibal**, its wing-shaped guard absorbing Fantasia to make the blade grow faster and more precise with each swing. Additional capabilities include broomstick flight, dimensional travel via an unidentified coffin to his hideout, enhanced senses for distinguishing energy sources, Fantasia-based physical amplification, and pain resistance. His combat tier is Town level in potency, durability, and striking strength, with Subsonic speed.

His primary relationship is with Seth, beginning antagonistically in Rumble Town after Grimm mistakenly identified Seth as an ally of the villain Hameline. After initial clashes, they collaborated to defend the town from cannon fire, with Grimm healing Seth's injuries. He later aided Seth, Mélie, and Doc in thwarting Hameline's destruction plot and escaping the Inquisition. These events forged mutual trust, leading Grimm to join their quest for the mythical Radiant. Narratively, he functions as a Jungian "shadow" archetype to Seth—representing repressed traits through ambiguous methods and offering guidance that challenges Seth's perspectives without imposing his own path.

Grimm's background remains largely undisclosed. His Rumble Town activities involved sheltering witnesses targeted by Konrad; initial secrecy and combativeness toward Seth stemmed from misinformation. After resolving the conflict and clarifying intentions, he allied with Seth's group. His broader history, including the origin of his bandages or infection, remains unexplored across official media.