From almost the very beginning of her career, Masami has sung themes for anime tv and movies. She is especially well known for her songs from Revolutionary Girl Utena, Slayers, Sorcerer Hunters, Di Gi Charat, Magic User's Club, Jungle de Ikou, Akihabara Dennou Gumi, Ray the Animation, He Is My Master and Yu-Gi-Oh! Duel Monsters. She has performed material for more than 50 singles and 20 albums to date (including her work with JAM Project and Chihiro Yonekura).
Okui currently hosts @Tunes, an anime music news program, on the Japanese anime television network Animax.
* 1993, released her first single "Dare Yori mo Zutto". This was for the anime OAV The Girl from Phantasia
* 1995, sang together with Megumi Hayashibara for TV anime Slayers. The two artists have become best friends since.
* 2003 - she teamed up with fellow artist Chihiro Yonekura to form the group r.o.r/s (an acronym for "Reflections of Renaissance/Sounds.)
* 2003 - Debuted as a member of the supergroup JAM Project with the single: "Little Wing". This song became the opening title track for the noted anime series Scrapped Princess.
* 2003 - Became the music producer of her own record label, evolution.