Masami Okui is a Japanese singer, lyricist, and composer whose career has been closely tied to anime music since her debut in the early 1990s. Born on March 13, 1968, in Itami City, Hyogo Prefecture, Okui began her career as a backup vocalist for artists including Yuki Saito, Tomoyo Harada, and Wink starting in 1989, and also provided backing vocals and danced for Yumi Matsutoya's tours until 1995. She made her own solo debut in August 1993 with the single Dare yori mo Zutto.

Okui is known for her involvement with numerous anime series, often performing opening and ending themes. Her songwriting credits are extensive, as she frequently writes the lyrics for her own songs and contributes to the music composition. One of her notable works includes the song Takarabako (Treasure Box), which served as the second opening theme for the anime series SHIROBAKO.

Her contributions to the Starship Girl Yamamoto Yohko franchise are substantial. For this series, she performed the opening theme Tenshi no Kyuusoku (Angel's Rest), the ending theme Ru-Ru-Ru, and the insert song eternal promise. She also performed Shake It for the franchise. These songs highlight her role as both a performer and theme song creator for the series. Additionally, she performed Souda, zettai as an opening theme for the same OVA series.

Okui has collaborated extensively with arranger and composer Toshiro Yabuki. Many of her early singles and album tracks, including Shake It, Souda, zettai, and the songs from her 1998 single Birth/Taiyou no Hana, were arranged and co-composed by Yabuki. The single Birth/Taiyou no Hana features the opening and ending themes for the anime Cyber Team in Akihabara, with Okui writing the lyrics for both tracks and composing the music.

Her career is also marked by significant collaborations with fellow voice actress and singer Megumi Hayashibara. The two performed the duet Get along as the opening theme for the Slayers television series, and also collaborated on Give a reason, which served as an opening theme for Slayers NEXT. Okui has also performed theme songs for franchises including Revolutionary Girl Utena (the opening theme Rondo -revolution-), Slayers, and Jungle de Ikou!. In 2006, she was a featured artist on the collaborative single OUTRIDE, which included many prominent anime singers.

Okui is also known for her membership in JAM Project, a supergroup of anisong singers founded in 2000, where she has performed alongside artists such as Hironobu Kageyama, Masaaki Endoh, and Hiroshi Kitadani. She has also been part of the unit r.o.r/s with Chihiro Yonekura. Her musical identity is characterized by a powerful and wide vocal range, energetic rock-influenced pop songs, and a hands-on approach to songwriting and production. In 2004, she founded her own record label, evolution, and has taken on producer roles for other artists. She continues to release new music, with singles such as God knows... from CrosSing appearing as recently as 2023. Her body of work, comprising dozens of singles and albums, has cemented her status as a significant and enduring figure in the world of anime music.