She became a professional singer in 1999. Her first successful audition was with I've Sound, a team of producers using the talents of various female vocalists for their productions—best recognized for their many dating sim and eroge game soundtracks. Since then, Kotoko has performed opening and ending themes for a few anime and has gained significant recognition from her two I've Sound-related album releases. Her second album, Glass no Kaze, released in June 2005 has been praised within multiple online communities. On October 13, 2005, she released her fourth maxi single, which featured a song from her Glass no Kaze album, "421 -a will-" and its B-side song called "Shuusou" (秋爽, The Refreshing Autumn Breeze), which is featured in her third album, Uzu-Maki.
Although not listed on her official Geneon website, Kotoko has actually released four albums. Her very first album was called, Sora o Tobetara, which was released in 2000. Many of the tracks on this album were later re-recorded for her first I've Sound album, Hane (羽 -hane-, Feather?), and was attributed as her first album. Her first I've Sound CD appearance was on the CD "Dear Feeling" (only released at "Comic Market 59".) with previous singer Aki. She then appeared on I've Girls Compilation Album Vol.3 "Disintegration", a series of albums with various songs from the I've Sound singers.
Kotoko's first official performance in North America was her highly successful American concert debut at Anime Expo 2005, followed soon after by the Kotoko Lax Tour. Now that her self-composed hybrid of pop and techno beats—sometimes pop—have crossed the Pacific, Kotoko's lyrics have elevated her presence among thousands of North American J-Pop/anime fans.