Kōga is a mononoke, or evil spirit, who appears as a young boy with asymmetric short white hair, brown eyes, pronounced canine teeth, and a single twisted horn that grows from the right side of his head when he uses his power. He dresses mainly in black clothing with white accents. He works alongside the mononoke Amagi and openly declares himself to be the man who will become the strongest mononoke. His primary motivation is to become the immortal king of mononoke, and to achieve that he plots to claim Rago, the legendary Black Star of Doom, as his own. Kōga is brash, energetic, and seemingly juvenile in his attitude, but he is driven by a clear and ruthless ambition. In battle, he demonstrates notable durability, able to withstand full-strength attacks from Reiji Kirihara and a weakened Rago with only minimal damage. His signature ability involves manifesting a large sword-like weapon from his own blood. Within the story, he serves as an antagonist, opposing Jiro Azuma and the Bureau of Espionage, and his actions are driven by his desire to usurp Rago's power for his own ascension.