Kubo was born on June 26, 1977 in Hiroshima Prefecture, where his father worked as a town council member. In elementary school, he had already decided to become a manga artist, due to reading the manga Saint Seiya. His first one-shot was "Ultra Unholy Hearted Machine", written for the Weekly Shōnen Jump in 1996. He wrote his first manga Zombiepowder, which was also published in Weekly Shōnen Jump in 1999. It ran a short 27 chapters before being canceled in 2000. According to the author's comment