Seiji Momoi became a sound designer at DATA EAST in 1990, working on games such as "Joe & Mac: Caveman Ninja" and "Heracles no Eikou III: Kamigami no Chinmoku". He left DATA EAST in 1993, briefly working at a music production company before going freelance in 1995.

In 2000 he started the music unit "Saikyosha", and has composed, arranged, performed and conducted across various mediums, including games, musicals, films and wind ensembles. In 2013, he rejoined GAMADELIC (the former DATA EAST in-house band) under the name Saint☆Peach.