Her most well known songs are "Arigatō..." (ありがとう..., Thank You) (which reached number 2 in Hong Kong when it was covered by Sammi Cheng) and "The Power of Smile" (which topped at No.

She is also recognized for her numerous contributions to anime/game soundtracks, the most notable being "Ai no Melody/Chōwa Oto (With Reflection)" for the film Origin: Spirits of the Past, "Follow the Nightingale" for the game Tales of Innocence, "Tatta Hitotsu no Omoi" for the anime Gunslinger Girl: Il Teatrino, "Dance of the Spirits" for the anime “The Ancient Magus' Bride” and "For Little Tail" for the game Tail Concerto.

Kokia often performs in Europe, basing her activities in Paris and releasing music through Wasabi Records, a subsidiary of Kazé.

)[citation needed] The leading single from the album, "Arigatō..." (ありがとう..., Thank You), found success in Hong Kong.

[8] Hong Kong entertainer Sammi Cheng covered the song, and released it as the eponymous track from her album "Arigatou" in October 1999.

Her single "Kawaranai Koto (Since 1976)" was used as the drama Itoshiki Mono e's theme song,[7] breaking Kokia into the top 50.

[14] Her Pony Canyon-era songs "I Catch a Cold" and "Shiroi Yuki" (白い雪, White Snow) were used in the soundtrack for the popular Chinese drama At the Dolphin Bay in 2003.

[16] Kokia's fourth album Uta ga Chikara (released in 2004) also found modest success, selling 20,000 copies.

[14] The biggest single from this album, "Yume ga Chikara," was used as the encouragement song for the Japan team at the 2004 Athens Olympic games.

[14] From 2006 onwards, Kokia began working in European markets, as well as taking greater control over her musical releases.

In January, she held her first European concert in Paris, and performed at the Midem music industry trade fair.

[7] In June 2006, Kokia decided to set up her own production company separate from Victor Entertainment, called Anco & Co., after desiring more creative control over her works.

[27][28] In 2004, on the TV show Daimei no Nai Ongaku-kai 21 (題名のない音楽会21), Kokia attempted to break the Guinness World Record for the longest note held.

Occasionally in songs, such as "Chōwa Oto" (調和　ｏｔｏ, Harmony, Sound) and "Follow the Nightingale," Kokia writes lyrics in code.

[30] In "Chōwa Oto," Kokia also has a separate code (the numbers 3 25 15 21 23 and 1) which correspond to the letters of the English alphabet (1=A, 26=Z) to write the song's name in wāpuro rōmaji (C Y O U W A).

[30] Violinist Kyoko Yoshida is Kokia's older sister,[citation needed] and also attended the Toho Gakuen School of Music.

[5] She has performed at a concert for drug abuse,[13] supported the Japanese Social Welfare Organisation (社会福祉法人),[5] and released a special charity single for the victims of the 2007 Niigata earthquake.

[7] She gave out 10,000 copies of a special EP, Music Gift, on the streets of New York City in memory of the attacks.