Un-ou is an S-Class ES (Encounter of Shadow-work) member within the Galactic Organization of Trade and Tariffs or its successors. He operates with his partner, A-ou, as one of the ES pairs enforcing galactic economic stability. Cynical, impulsive, and relishing the danger of his missions, Un-ou carries a competitive grudge against Éclair and Lumière from their time as fellow peace officers, a rivalry persisting during their fugitive status. This antagonism originated earlier, during Un-ou's mercenary days before joining GOTT, when he and A-ou frequently clashed with the pair. Despite this hardened exterior, he maintains a serious commitment to his duties.

His ES ability, "Amazing," detects and tracks life energies across distances, serving as a sensory power to locate targets or threats, complementing A-ou's long-range vision. Un-ou possesses bright orange eyes and forest-green hair. He cross-dresses, wearing women's clothing and undergarments, a practice he justifies as beneficial for missions. He physically presents as 14 years old, though his chronological age may differ. The names Un-ou and A-ou derive from Japanese and Sanskrit Buddhist lore, specifically referencing the two Deva Kings, reflecting the series' thematic conventions. His background as a mercenary defines his integration into GOTT's shadow operations.