He was caught by the public's eye in the play, Twelfth Night, which was directed by Michael Pennington. He played the role of Sebastian.
Koyama's first production with Haiyuza Theatre was The Idiot, in which he played the role of a servant.
He's 5'6, weighs 143lb, and has a Blood type of O.
Several of his dubbing roles, from the American market to the Japanese market, included voicing for characters played by George Clooney. In fact, after his success at dubbing for Clooney's character on the hit TV drama ER, Koyama has dubbed for every movie Clooney has been in since "Peacemaker".