Alastor, known as the Flame of Heaven, is the Crimson Realm’s God of Retribution, presiding over judgment and condemnation. He is a Crimson Lord whose power is considered unmatched among his kind, earning titles such as the True Demon God of the Crimson Realm. His true form resembles a massive minotaur with powerful limbs, horns, and large wings like the night sky, his body engulfed in destructive flames that burn everything to ashes. His voice echoes like distant thunder.

Alastor is contracted to the Flame Haze Shana through the divine vessel Cocytus, which manifests as a pendant with a black sphere encircled by crossing gold rings on a silver chain. Previously, he was contracted to Mathilde Saint-Omer, with whom he shared deep mutual respect and love. During the Great War against the Crimson Denizen organization Töten Glocke, Mathilde sacrificed herself to summon Alastor using a ritual called Tenpa Jōsai, which consumes surrounding Denizens for power. After her death, Alastor resided within the floating fortress Tendōkyū and, alongside Wilhelmina Carmel and Merihim, searched for a pure Flame Haze dedicated solely to their mission. After centuries of failed candidates, they found Shana, whom he deemed the perfect vessel.

Initially, Alastor shared Shana’s indifference toward humans and Torches, viewing them as insignificant objects, and showed confusion about human social norms such as modesty. He prioritized combat training over social development, a lapse he later acknowledged. Over time, he evolved into a protective father figure for Shana, recounting stories of Mathilde and supporting her emotional growth. When Shana suffered severe injury, he assumed his true form to annihilate the perpetrator without remorse. During the Second Great War, he opposed the Snake of the Festival’s merger with Yuji Sakai and rejected Yuji’s philosophy of self-punishment. After overpowering Yuji and witnessing his transformation into a solid existence, Alastor departed with Shana and Yuji to Xanadu to oversee its stability.