Tarōja Onimaru is a half-demon, half-human master of Jukondō, a discipline encompassing forbidden curses and dark arts. His hybrid nature endows him with abilities bridging supernatural realms, guarded by the deity Mahakala (Daiankokuten). This duality establishes him as a dark, esoteric counterpoint to the protagonist Kujaku's light-based Tantric Buddhism.

He operates as a mercenary, offering his services to any side providing adequate compensation. This pragmatic approach sometimes leads him to ally with Kujaku and others against mutual supernatural threats, despite differing methods and morals. For example, he partners with Kujaku to stop the necromancer Tatsuma, who seeks to unleash a universe-destroying demon from a stolen statue.

In combat, Tarōja wields forbidden techniques and curses, reflecting his Jukondō mastery. His role consistently involves confronting entities threatening global stability, leveraging his unique half-demon powers and occult knowledge.