Koichi is a teenage boy of average build, though he's depicted as shorter than that. He wears a notably unmodified student uniform, otherwise preferring leisure wear. Koichi first keeps his light hair neatly combed back. During his confrontation with Tamami, it gains the tendency to rise into spikes when he is excited (producing a look similar to that of Dragon Ball Z character Gohan at Super Saiyan 2 during the Cell Games). Towards the end of his confrontation with Yukako he suddenly cuts his hair, producing a flat-top, which spontaneously grows out again into spikes during his battle with Yoshikage Kira. The color of his hair varies throughout medias, the most common schemes being blond, blue, or silver.