Kouichi is Shinichi's older brother and a secret agent for an organization called Phoenix, whose cover is a manga artist. His primary adversary is Interspy, though he also fights against others as well.

Kouichi sometimes uses guns, but primarily relies on martial arts, and his watch, which contains a small hammer and chain, a radar, and a flashlight, which can also be used as a beam to blind his opponents. His pipe also contains a smoke gas which can conceal his whereabouts. Within Phoenix, he is known as Agent P77. Kouichi joined Phoenix in order to avenge the death of a friend (who had previously been Agent P77) who had been killed by Interspy.