Shūichi Akai (赤井秀一, あかいしゅういち ?) is a fictional character in Case Closed. He is an American of Japanese descent who wears a black tuque and smokes heavily. Shūichi Akai is a man of few words and his phrases are filled with euphemisms and metaphors to disguise his true motives. He first appears as a bus passenger during a bus hijacking case in volume 29 of Case Closed. He is a mysterious character who stalks Richard Moore's detective agency for unknown reasons. Several scenes in the series imply that Rachel Moore has met him before. His true motives and his identity are two of the biggest mysteries in Case Closed. He tries to avoid Anita Hailey of whom he has a photo on his pick-up truck dashboard.

In the anime, he is voiced by Shuuichi Ikeda, and his name is most likely a reference to one of Ikeda's earlier roles: Gundam's Char Aznable. Char is known under the nickname "the Red Comet" and the first kanji in Akai is 'aka' (red). His name could also be an homage to Akai-san, a mysterious character who appeared in one of Edogawa Ranpo's Akechi Kogoro novels: Nanimono

Source: Wikipedia