Born in Tokyo in 1957, Kou Otani was born into the world of music by his parents who were into modern dance. He studied classical and modern music at Nihon University and took lessons in Jazz1. After graduating Otani became a founding member of the company Imagine in 1986. His earlier work includes scoring the music to the popular anime series Future GPX Cyber Formula (1994-1995), which had lengthy running spans on television. In 1995, Otani composed the music for the film Gamera: Guardian of the Universe and later Gamera: Attack of Legion, both part of the cult classic monster series. In the same year, he composed his first video game title, Philosoma, an early, obscure PlayStation shooter, and began to work on the highly praised Mobile Suit Gundam Wing series (1995-1996).
Continuing his successful run, he composed the majority of the anime series Wild Arms: Twilight Venom (1999-2000), and also the score for the movie Gamera 3: Awakening of Irys (1999). The following year he provided the music for the video game flight simulator, Sky Odyssey. The year 2001 was yet again busy for Otani, he was chosen to create the score for Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack, the series Zoids: New Century Zero. In 2002, he scored the short, but artistically brilliant series Haibane Renmei created by Yoshitoshi ABe and animated by Studio Radix. It was only late 2005 where he composed his first major video game title, Shadow of the Colossus, known for its epic score. He also contributed the music for the anime series Shakugan no Shana, its two sequels, OVA and film (2005, 2007, 2009, 2011, 2012). Otani also composed the soundtrack to the animation adaptation of Australian author Emily Rodda’s children novel series, Deltora Quest in 2007. In 2008 he composed the score for the anime series Gunslinger Girl -Il Teatrino-. A year later he scored the anime Tokyo Magnitude 8.0, a story about a magnitude 8.0 earthquake hitting Japan in 2012.
Otani appeared at Eminence's Australian orchestral concert A Night in Fantastia 2007: Symphonic Games Edition where three pieces from Shadow of the Colossus were performed. He also appeared alongside AIKA in a smaller concert later that year titled Unearthing Eden
The sounds of AINARU. He later returned to Australia to perform a suite from Shadow of the Colossus in A Night in Fantastia 2009 with his fellow band members from Hyper Little Toy's.