After graduating from university, Yamamoto became employed at the Kyushu branch of Yamaha, composing music for various commercials and creating arrangements for the company's music contests known as the Popcon and the World Popular Song Festival. His departure from Yamaha enabled him to write music for a wider range of works such as plays and TV dramas. At that time, he became involved with the Dragon Ball series and was put in charge of the composition for several video games and writing arrangements for complete album releases. In the more recent years, he became one of the executives of 59's Laboratory, a music production company founded in 2004, has been producing live concerts and started to provide his music services as a freelance composer.