Koyanagi is an inventor and Tadashi's uncle.
Koyaganagi is an aging man with a morose face He has wavy dark black hair and sports a medium length goatee.
Koyaganagi is a slightly obsessive and neurotic inventor. Ms. Yoshiyama acts as his lab assistant. In the OVA, he tries to figure out what has caused the fish to begin walking. He compares the smell of a corpse to that of the creatures. While dissecting a captured death stench fish he notices that although the fish is dead, the walker's legs still function. When he got too close, the legs then clamped onto him. He cut off his arm to prevent the infection from spreading to the rest of his body. He is fascinated by the machine, not caring that he lost an arm to it. He is mortally wounded when he is stabbed by the spider-like leg of Kaori's walker.