Alastor is a Crimson Denizen hailed as the "Flame of Heaven" and stands as one of the ruling Gods of the Crimson Realm. This powerful entity forges a contract with the Flame Haze called the "Flame-Haired, Blazing-Eyed Hunter," later known as Shana. He dwells within her, granting power and offering guidance in the struggle against those who threaten the balance between worlds.

Alastor appears throughout the series' many adaptations, including the central television seasons, original video animations, and cinematic releases. In one theatrical feature, a special segment titled "The Sovereign Carmel-san" includes the Flame Haze Wilhelmina Carmel, who alludes to Alastor’s presence and function amid wider events.

His influence also reaches into parody shorts under the title "Shakugan no Shana-tan," which present a super-deformed rendition of Shana and frequently include lighthearted depictions of Alastor's engagements.