Amano Jyaku, a half-demon, half-human hybrid exiled from the man-beast world to Earth for crimes against the Elder and his daughter Mimi, dedicates himself to finding the Chōjin—a prophesied figure meant to bridge the human, demon, and man-beast realms. His motives and tactics diverge between adaptations: the manga frames him as a cunning, self-serving opportunist who exploits women through deceit, leveraging false claims about his demon-slaying sperm. The anime reimagines him as an idealistic devotee of the Chōjin prophecy, striving to forge a harmonious "Land of Eternity" until mounting contradictions erode his convictions.

His path entwines with clashes against adversaries such as Münchhausen II, a Nazi occultist reviving the ancient Kyō-Ō. These confrontations pit him against forces manipulating figures like Takeaki Kiryū, host to the Kyō-Ō and cousin to Tatsuo Nagumo, the Chōjin’s chosen vessel. Personal stakes intensify when his sister Megumi develops a romantic bond with Takeaki, intertwining familial loyalty with apocalyptic warfare.

While the manga fixates on his morally gray treachery, the anime traces his ideological unraveling—from unwavering prophecy adherent to reluctant combatant in cataclysmic battles, including a skyscraper showdown in Shinjuku. Allies like Kuroko, a steadfast tribesman, anchor his fractured pursuits. Across iterations, his arc orbits his exiled heritage, fluctuating between redemption and ruin, with his fate shifting alongside the medium’s tone—manga underscoring his amorality, anime dissecting the fallout of shattered dogma.