Iwashiro has composed the music for many Japanese television series and films.
He has composed for both Red Cliff films, Shinobi: Heart Under Blade, Azumi, The Prince of Tennis, Rurouni Kenshin: The Motion Picture, and the Korean film Memories of Murder.
He was also lead composer for the Capcom video game Onimusha 2: Samurai's Destiny.
[citation needed] Iwashiro has often led the Tokyo Metropolitan Symphony Orchestra for his soundtracks, including the 2005 taiga drama Yoshitsune and 2008 film Red Cliff.
[citation needed] He also composed the opening song for a video game, Breath of Fire IV (2000).