Koinuma has middle part, straight sandy hair that covers his ears and reaches to his chin. Like the other members of his unit, in his trion body he wears dark pants, a lighter jacket with a high collar, and boots of the same color, as well as dark-rimmed goggles with square, protruding lenses.
As a B-rank agent, Koinuma should be more skilled than a C-rank trainee. His unit's foremost tactic is a combined attack which sees the three Shooters focusing their Full AttackHound on a single target. This technique, called Hound Storm, was extolled by Ken Satori as a very powerful attack. However, the whole unit was easily defeated by the combined might of Chika and Yūma without managing to put up any form of resistance.