As one of the leading vocalists representing the music creator collective I’ve, KOTOKO made her major debut in 2004 with the album 羽-hane-. Her song being, the opening theme for the TV anime Shakugan no Shana, debuted at No.4 on the Oricon Weekly Singles Chart, and many of her works have since ranked highly on the Oricon charts.

In Japan, she has performed at venues including Yokohama Arena and Nippon Budokan, as well as holding solo concerts across Asia. She has also appeared at major anime and game song events, captivating fans with her versatile vocal performances.

In April 2020, she released the 10-CD box set KOTOKO’s GAME SONG COMPLETE BOX「The Bible」, featuring 134 game songs she worked on, which debuted at No.4 on the Oricon Weekly Album Chart. In 2021, INTERNET OVERDOSE, a collaboration with Aiobahn, became a smash hit and expanded her fanbase among Gen Z listeners.

Starting in April 2023, to celebrate the 20th anniversary of her major debut, she embarked on her second nationwide tour covering all 47 prefectures of Japan. In September of the same year, she released the commemorative album リデコレイト・マイセルフ. In July 2026, she is scheduled to release KOTOKO’s GAME SONG COMPLETE BOX「The Bible2」. Beginning in September 2026, she is also scheduled to hold an 18-show album release tour both in Japan and overseas. Even after celebrating her 20th anniversary since her major debut, she continues to stay highly active.