Originally from Tokyo, Kei IWASAKI began a solo career in 2001, he asked Kyo Yoshizawa, a childhood friend to accompany him on drums, and Masayuki Nakauchi him as a session bassist. All the "trio" released his first album, the solo project and start becoming an official group; SEKAIICHI is born! The group is building a solid reputation by turning all over Japan (300 concerts in 3 years), they signed to Toy's Factory in 2005. In December 2006, Kentaro IZUMI joined as bassist, lead guitar becomes Masayuki. In 2010, the group signed with AVEX.