Reiot Steinberg combats demonic entities spawned by magical corruption as an unlicensed tactical sorcerist. To prevent his own transformation into a demon during spellcasting – accelerated by accumulated curse contamination with each magic use – he binds himself in specialized armor called a "Mold" or "straitjacket." This armor constrains his human form while permitting controlled sorcery, typically channeled through magically enhanced railguns effective against demonic threats.

His actions are rooted in profound personal trauma and guilt. Fragmented, stylized flashbacks depict him killing his own teacher under obscured circumstances, an event forging his nihilistic worldview and self-perception as a "mass murderer." He also caused the deaths of another child's parents, subsequently becoming the guardian of that child, Kapelteta Fernandez. Kapelteta manifests physical deformities from magical exposure, and Reiot shelters her while wrestling with remorse over his role in her condition. His relentless demon hunting intertwines with atonement for these sins.

Reiot maintains a contentious relationship with the regulatory Magic Administration Bureau. It officially condemns his unsanctioned vigilantism yet tacitly relies on his effectiveness. Colleagues like Inspector Nerin Simmons scrutinize his motives, while figures such as Isaac Hammond openly resent him, partly due to Isaac's reverence for Reiot's deceased teacher. Reiot's solitary and detached demeanor reflects his internal struggle against despair and the constant risk of demonic transformation. He prioritizes neutralizing immediate threats over bureaucratic protocols, often resulting in collateral damage that cements his outsider status.

Physically, he possesses gray eyes and shoulder-length purple hair, presenting an adult appearance. His typical field attire includes practical clothing like a coat and sunglasses, worn alongside his signature armor.