Amano Jaku is a hybrid entity, originally half-demon and half-human in the manga, though anime adaptations depict him as part of a distinct man-beast race. Banished from the demon realm for transgressions involving the Great Elder's daughter, Mimi, he receives a mandate to locate the Chōjin—a prophesied entity destined to unite or transform the worlds.

His manga portrayal emphasizes a manipulative and lecherous persona, frequently deceiving women into sexual encounters by falsely claiming his semen repels demons. Conversely, the anime presents a more protective and mission-driven role, tasking him with safeguarding Tatsuo Nagumo, the human vessel for the Chōjin's rebirth. His anime motivations stem from a belief in the Chōjin's promise to forge an eternal, harmonious realm spanning the human, demon, and beast worlds.

Within *Urotsukidōji III: Return of the Overfiend*, Amano Jaku navigates a post-apocalyptic landscape reshaped by the Chōjin's prior emergence. He investigates the premature birth of the Chōjin's nemesis, the Lord of Chaos (Kyo-Ō), in Tokyo under Caesar's tyrannical rule. This investigation pits him against Caesar's regime and its enslavement of the Makemono, a new demon-beast race. He allies with Buju, a former marauder turned guardian of the Kyo-Ō, to confront threats against the nascent Chōjin in Osaka, reflecting his ongoing commitment to cosmic balance amidst widespread chaos and tyranny.

Across all media, Amano Jaku endures for centuries, underscoring his resilience and pivotal role in the cosmic conflict. His character evolves from self-interest in early manga iterations toward a more determined protector in later anime arcs, while his core function as a mediator between realms remains consistent.