Kyō Hyūga is a Japanese male who begins his career as a bodyguard for Shichisei Hiruma before advancing to section manager at Ichi Security. His first documented appearance takes place during the Annex I Arc in 2619 A.D., where he stands guard outside a bar alongside Someya while Hiruma speaks with Honda Kou. During this assignment, Hyūga alerts Someya that Annex I has activated "Plan Delta." Their conversation touches on the A.E. Virus outbreak and the deteriorating state of infected individuals, specifically mentioning Sakurato Harukaze as beyond recovery. While maintaining their post, Hyūga and Someya repel an attack by unidentified assailants attempting to kidnap Honda. Hyūga dispatches the attackers with swift efficiency, addresses them in Russian, and confirms their nationality through their reactions.

Hyūga possesses genetic modifications derived from the western diamondback rattlesnake, granting him a specialized sensory system that detects infrared heat signatures across his entire body. This ability allows him to scan multi-level structures comprehensively, identifying occupancy from top to basement. He also exhibits enhanced respiratory capacity, expanding his chest cavity to increase lung volume approximately sevenfold. This adaptation enables extended breath-holding to avoid airborne hazards and amplifies his vocal output to levels capable of rupturing human eardrums.

In combat, Hyūga demonstrates expert marksmanship, wielding dual firearms simultaneously with high precision. He operates as a quick-thinking tactical analyst with rapid reflexes, evidenced by his support during Hongou's confrontation with Jinjen Von Vinland.