Koumei is a Police inspector from Nagano. He is a childhood friend and rival of Inspector Yamato.

Koumei and Yamato Kansuke were both students at the same elementary school, which is where the two met. Koumei's exploits were so well known that a book about a child who solved a case in a elementary school, titled "Komei-kun from Second Second Grade Class A!" was based off of him, while another character in the book was based off of Yamato. Koumei cherishes the book, keeping it in the glove compartment of his car, as the author was a friend of his who died. He was originally a high ranking inspector in Nagano, until he abadoned his job briefly to try and find Yamato when he was left for dead in the snow during a case. After Koumei found the suspect, and helped save Yamato, he was downgraded as an inspector in a local force in Nagano. Later it is revealed that he has effectively returned to the main headquarters.

Komei is generally shown to be calm and well-mannered, in contrast to the quick-tempered Yamato. According to Yamato, Komei tends to ignore others completely while investigating, and sometimes goes out of his jurisdiction to try and solve a case. He will even put his life on the line if he has to. The rivalry between Yamato and Koumei is mostly a friendly one, in which they see who can solve the case first, and Yamato has tried to get Koumei back onto the regular force. Also, Yamato has been willing to go into a burning building to save his life.