OVA
Description
Alastor, bearing the titles "Flame of Heaven" and "God of Retribution," is a Crimson Lord of the Crimson Realm governing judgment and condemnation. He commands immense fear among Denizens as one of the realm's mightiest lords. Alastor forges contracts with Flame Hazes, humans dedicated to protecting the world from Denizens who consume human existence. His power manifests through the divine vessel Cocytus, which appears as a pendant while bound to his current contractor, Shana.

Initially displaying apathy towards humans, Alastor dismisses Torches—remnants of consumed humans—as insignificant objects. This view leads him to question Shana's embarrassment about nudity in front of Yūji Sakai, likening it to being naked near inanimate things. He acts as a paternal figure to Shana, having guided her development into the "Flame-Haired Burning-Eyed Hunter." He recounts tales of his past contractor and lover, Mathilde Saint-Omer, who sacrificed her life to summon him during the "Great War" using the Tenpa Jōsai ritual, obliterating the Denizen forces led by Asiz of Töten Glocke.

Alastor's personality blends regal authority with occasional difficulty grasping human social nuances. He speaks formally yet exhibits discomfort with topics like human reproduction, deflecting explanations. He acknowledges failing to teach Shana social skills during her training, recognizing this oversight. Despite his stern nature, he permits Shana's growth and independence, especially as her bond with Yūji strengthens.

His protective instincts surge when Shana faces mortal peril. He assumes his true form—an imposing, flame-wreathed minotaur-like entity with wings and burning eyes—to annihilate threats, exemplified by killing Friagne after Shana's injury. Allies and foes alike note this ferocity; the Snake of the Festival warns that harming Shana invites Alastor's vengeance. During the Bal Masqué conflict, he intervenes against Hecate's attempt on Shana, condemning her shortsightedness regarding consequences.

Alastor's relationship with Shana evolves. He starts using her given name for practicality, eventually adopting it habitually. He tolerates Yūji's presence due to Shana's attachment, though criticizes Yūji's initial combat weakness. In the Second Great War, Alastor opposes Yūji after his merger with the Snake of the Festival, collaborating with Shana and Margery Daw to restructure the Unrestricted Spell and impose a Law protecting humans in Xanadu. When Yūji activates Lamie's Unrestricted Spell to restore consumed humans, Alastor and Shana reject his philosophy of self-punishment, overpowering him in battle.

Following the conflict, Alastor accompanies Shana and Yūji to Xanadu, aiding efforts to establish coexistence between humans and Denizens. His true form, concealed within flames, contains a dark mass, and his voice resonates like distant thunder. Alastor's existence embodies the tension between retribution and growth, concluding his journey by supporting Shana's new purpose beyond eternal conflict.