OVA
Description
Atun originated as a powerful demon locked in a longstanding, unresolved rivalry with the demon hero Amon, fostering a deep-seated grudge. He possessed avian traits: maroon feathers, dark purple skin, yellow pupil-less eyes, large black wings, and limb talons capable of shifting position for combat or extending to pierce enemies. His abilities included flight, strength and speed matching Amon's, channeling energy into destructive blasts, and tracking fast targets via a bird-like headpiece.

Seeking to merge demonic power with cybernetics, the human scientist Dr. Adams Teufel collaborated with Atun. As part of the Cyborg Daemon project, Atun agreed to possess the comatose youth Seth, transformed into Cyborg 0018. This fusion enhanced Atun's natural abilities with cybernetics, including a speed accelerator and self-repair functions. Upon awakening in Seth's body, Atun immediately killed Dr. Adams for attempting control, declaring the scientist no longer useful [citation:].

In this merged state, Atun manifested a muscular humanoid form with diluted blue eyes, red facial markings, and black feathers covering his lower body. Targeting Devilman (Amon's human host) to settle his ancient rivalry, he battled using combined demonic and cybernetic powers. During a confrontation, an anti-energy wave from Cyborg 001 and Eva (Seth's sister, Cyborg 0015) disabled his self-repair systems but triggered an unexpected further fusion. This transformed him into Azazel, an angelic entity with white hair and heightened destructive power that effortlessly killed several High-Teen Number Cyborgs.

Eva Maria used astral projection to separate Seth's soul from Azazel, reverting the entity to Atun's true demon form, now stripped of cybernetic enhancements and regeneration. Atun persisted in his assault but was weakened during a final energy-channeling attack by Cyborg 009's intervention. This allowed Devilman to incinerate him completely with fiery breath.

The name "Atun" derives from the Egyptian creator deity Atum, reflecting his thematic parallel to Amon (another Egyptian god-name). His design and role incorporate nods to other Devilman mythos entities, resembling early Amon depictions and adopting Satan-like traits as Azazel.