Crystal Kay began singing for TV commercials as child from the age of 4. At the age of twelve, Crystal Kay signed to the label Epic Records in Japan when a jingle she recorded for TV CM for Vitamin water garnered attention. One year later the jingle was expanded into her debut single “Eternal Memories”, on July 1, 1999. Despite peaking at number 47, “Eternal Memories” has since become Crystal Kay’s eighth best-selling single. 1999 saw the release of two more singles, “Teenage Universe (Chewing Gum Baby)” on September 8 and “Komichi no Hana” on November 3, the former peaking at number 47 and the latter at number 80.

Crystal Kay is considered a pioneer for interracial acts in Japan. She debuted in 1999 when R&B began to take off in Japan thanks to local acts MISIA, Double and Hikaru Utada. Her success paved the way for the mainstream success of many mixed-race artists in the mid-2000s (decade) such as Thelma Aoyama and African-American/Japanese enka singer Jero.

Crystal Kay’s debut studio album, C.L.L Crystal Lover Light was released on March 23, 2000. This album is noted by fans to have a more indie and acoustic feel as opposed to her later albums which mainly come under the genres of pop and R&B. Crystal Kay was only 14 years old when this album was released.

After a year-long period of inactivity, Crystal Kay returned to the music scene with the single “Lost Child”. The single, which was a collaboration with Shinichi Osawa and Hiroshi Fujiwara was released on February 15, 2001 and reached number 55 on its debut week. Despite Crystal Kay only being credited as a featured artist on the song, it was still featured on her next album, 637: Always and Forever. Her fifth single “Girl’s Night” came three months later on May 9, 2001. The single saw the introduction of urban influences in Crystal Kay’s music. Despite this new style, the single peaked at number 100. One of the b-sides, “Make Me Whole” was a cover of the Amel Larrieux song of the same name. Crystal Kay’s next single, “Ex-Boyfriend”, was released on July 4, 2001. It featured rapper Verbal of M-Flo. The single was a success for Crystal Kay, peaking at number 44, and became her best selling single at the time of its release. Crystal Kay released her sophomore effort on August 22, 2001, 637: Always and Forever. The album became Crystal Kay’s first album to reach the top twenty of the Oricon chart when it debuted at number 19, and sold 15,640 copies in its first week. Crystal Kay finished off 2001 with her seventh single, “Think of U”, released on November 28, 2001. The single was Christmas-themed. It debuted and peaked at number 60.

Nine months after her last single, Crystal Kay released her eighth single, “Hard to Say”, on August 7, 2002 and sold over double than her previous best selling single, “Ex-Boyfriend”. It became her first top thirty single when it debuted peaked at number 26 on the Oricon chart. The single was followed by the release of Crystal Kay’s next single “Girl U Love” and her third studio album Almost Seventeen, on October 23, 2002. Almost Seventeen became Crystal Kay’s breakthrough album, exceeding expectations and debuting at number 2 on the charts behind Mai Kuraki, selling 51,360 in its first week. The album spent a year on the charts, quickly being certified platinum by RIAJ. Three months later Crystal Kay released “Boyfriend (Part II)” on January 22, 2003. It peaked at number 23. Her next single came five months later, and was another collaboration with M-Flo. The single, called “I Like It”, was released as “Crystal Kay loves m-flo” and was notably the first in a long-running hit series for m-flo. It was also Crystal Kay’s first top ten hit.

“I Like It” peaked at number 8, becoming Crystal Kay’s first top ten hit and eventually sold around 50,000 copies. Another single, “Candy” was released a month before her fourth studio album, 4 Real, on October 22, 2003. “Candy” debuted inside the top thirty of the Oricon charts at number 21, her fourth single in-a-row to do so. 4 Real was released on November 27, 2003 along with Crystal Kay’s thirteenth single, “Can’t Be Stopped”. 4 Real debuted at number 6 on the charts behind household names in Japan such as Aiko, Do As Infinity and Mika Nakashima and sold 86,310 copies in its first week.

Crystal Kay’s debut English-language album, Crystal Kay (released as Natural: World Premiere Album in Japan), was released several weeks before 4 Real on November 7, 2003 in Asian territories including South Korea, Taiwan, Hong Kong and Thailand. The album was her first to be released outside Japan, and compiled English language songs from her previously released albums and singles, such covers of Gladys Knight, Cyndi Lauper and Judy Garland songs.

On May 12, 2004, released her fourteenth single, “Motherland”, the first of two that year. “Motherland” was used as the third ending theme for the anime adaption of Fullmetal Alchemist. It was the ending theme from episodes 26 to 41. The single debuted at number 9 on the Oricon chart, her second single to debut in the top ten. Just under two months after “Motherland”, Crystal Kay released her first compilation album, CK5, which was released on June 30, 2004, featuring a selection of tracks from Crystal Kay’s four previous studio albums, as well as her latest single, “Motherland”. The album celebrates Crystal Kay’s fifth anniversary since the release of her debut single “Eternal Memories” in 1999, hence the title. CK5 peaked at number 2 on the weekly chart and charted for 49 weeks, eventually being certified platinum by RIAJ. Another single, “Bye My Darling!” was released on November 17, and peaked at number 40 on the Oricon chart. It was Crystal Kay’s final release of 2004.

The single “Kiss” started off 2005 for Crystal Kay. It was released on January 26, 2005 and peaked at number 10 on the Oricon chart. The single had longevity at eventually became her second best-selling single. “Kiss” was the CM song for NTT DoCoMo “Music Porter”. “Kiss” was written by the same songwriter of the ballad “Yuki no Hana” by Mika Nakashima. Crystal Kay’s fifth studio album, Crystal Style followed two months later on March 2, 2005. The album debuted at number 2 and sold 296,756 copies. The album became the 44th best-selling album of 2005 in Japan.

Crystal Kay released her seventeenth single, “Koi ni Ochitara”, on May 18, 2005, which was used as the theme song for the drama Koi ni Ochitara: Boku no Seikō no Himitsu. The single is currently the best-selling single of her career, selling 295,456 copies to date and Crystal Kay has stated that it changed the focus of her career away from R&B and towards J-Pop. In its first week it sold 73,717 copies, in its second week it dropped to number 4 and sold 51,546 copies, and in the third week it fell one place to number 5, selling a further 38,302 copies. Crystal Kay’s next single was a collaboration with the R&B duo Chemistry called “Two as One”. The single was released on October 5, 2005 and peaked at number 2 on the Oricon charts, much like “Koi ni Ochitara” earlier that year. “Two as One” was released as Crystal Kay × Chemistry.

On February 8, 2006, Crystal Kay released “Kirakuni” / “Together”, her nineteenth single and the second A-side to be sung entirely in English. This single was recorded in the U.S. with producers Jam & Lewis, who are known for working with the likes of Crystal Kay’s idol Janet Jackson and Mariah Carey. Crystal Kay has stated that working with them was the personal highlight of her career and was landed on Crystal Kay as a surprise by her management. The recording took place over a hectic 3 nights in Los Angeles.

The second A-side “Together” was used as the theme song in Japan for the 2006 Winter Olympics in Turin. The single debuted at number 27. Two weeks later Crystal Kay released her sixth studio album Call Me Miss… on February 22, 2006. In its first week, Call Me Miss… debuted at number 2 on the Oricon chart as well as number 9 on the World Album Chart, selling 116,050 copies that week. It has since been certified platinum by RIAJ and was the 50th best selling album of 2006 in Japan.

For her eighth studio album Color Change! Crystal Kay had songs produced by Bloodshy & Avant and Jam & Lewis. Crystal Kay had previously worked with Jam & Lewis in 2006. The album was released on August 6, 2008. The title Color Change! reflected from Crystal Kay’s graduation from Sophia University that year. Color Change! peaked at number 6 on the Oricon daily chart and number 8 on the weekly chart, selling 15,519 copies in its first week. The album sold 33,290 copies after seven weeks on the charts. Color Change! was eventually certified gold by RIAJ. Color Change! was the 289th best selling album of 2008 in Japan.

After about a years hiatus, Crystal Kay returned to the music scene with the single “Kitto Eien ni”, which was released on January 17, 2007. “Kitto Eien ni” was used as the ending theme of the film Boku wa Imōto ni Koi o Suru, starring Jun Matsumoto. The single debuted at number 12 and charted for seven weeks, selling 19,615 copies. Crystal Kay’s twenty-first single, “Konna ni Chikaku de…”, was released on February 28, 2007. It was used as the ending theme to the anime adaption of the manga Nodame Cantabile. The single debuted at number 14 on the Oricon chart and charted for eight weeks, selling 15,158 copies to date. “Konna ni Chikaku de…” was performed live for the special Nodame Orchestra concert at the Tokyo International Forum on the single’s release date. Another single, “Anata no Soba de”, was released on May 16, 2007. The single only featured one track and thus was sold at the lower price of ¥525 in Japan. This single was the CM song for Menard Facial Salon. Crystal Kay released her seventh studio album All Yours a month later on June 20, 2007.

On November 28, 2007, Crystal Kay released her first EP, Shining. The EP had a Christmas theme and featured the title track “Shining” as well as a second new track “Snowflake” and the previously released tracks “Happy 045 Xmas” and “No More Blue Christmas”, originally featured on Natural: World Premiere Album. It debuted at number 21 on the Oricon chart. “Shining” was used as the CM song for “PARCO X’MAS 2007” throughout the Christmas period. Crystal Kay also starred in the commercial, in which she was seen “flying” on a reindeer.

The collection debuted at number 2 on the Oricon Daily Chart, and sold almost 30,000 copies that day alone, and ultimately dropped to number 3 on the Weekly Chart, behind Superfly’s Box Emotions and the second week sales of Arashi’s All the Best! 1999-2009. It sold 87,669 copies that week. This is Crystal Kay’s best peak position on the Oricon Chart since All Yours in 2007, as well as her best first week sales since Call Me Miss… in 2006. Crystal Kay finished off the year by releasing her first remix album The Best Remixes of CK on December 16, 2006.

On March 3, 2008, it was revealed that Crystal Kay was chosen to sing the theme song to the 2008 Pokémon film Giratina to Sora no Hanataba: Sheimi. She also played the voice of “Nurse Joy’s Chansey” in the film. The film’s producers had apparently been considering the singer since 2001, when she sang “Lost Child” with Shinichi Osawa and Hiroshi Fujiwara for the soundtrack of the film Satorare. As expected a single was released. However, it was not the recently announced Pokémon theme song, but a different single entitled “Namida no Saki ni”. “Namida no Saki ni” was released on June 11, 2008. It was Crystal Kay’s first single in over a year, since the release of the single “Anata no Soba de” on May 16, 2007. “Namida no Saki” was used as the CM song for Tully’s Coffee commercials throughout June 2008. This song exhibited a new, pop-rock sound for the singer. The single debuted at number 29 on the Oricon daily chart and eventually debuted at number 42 on the weekly chart. To date, the single has sold 3,587 copies. One month later on July 16, 2008, the Pokémon single, “One”, was finally released. “One” debuted at number 25 on the daily chart and debuted at number 32 on the weekly chart, selling 2,237 copies. To date, “One” has sold 6,522 copies.

Crystal Kay graduated in Sociology from Sophia University in 2008, allowing her to concentrate on her career full-time.

“After Love” was written by Craig McConnell and Canadian artist Shobha, with Japanese lyrics by Crystal Kay. “Girlfriend”, featuring the Korean artist BoA with whom Crystal Kay is reportedly close friends, was used as the image song for the Japanese dubbed release of the feature film He’s Just Not That Into You starring Jennifer Aniston and Ben Affleck. The single’s b-side, “Deaeta Kiseki”, was released digitally in December 2008 and was also used as the CM song for Tully’s Coffee that month. “After Love (First Boyfriend)” / “Girlfriend” was Crystal Kay’s second double A-side single, and her first since “Kirakuni” / “Together” in 2006. The single landed on the Oricon Daily Chart at peak position number 21 and on the Oricon Weekly Chart at number 31.

On February 18, 2009, Crystal Kay was a featured artist along with Verbal of M-Flo on the song “Universe” with South Korean singer BoA from her single Eien/Universe/Believe in Love. The single peaked at number 8 and has sold 21,789 copies. On May 15, 2009 it was revealed that Crystal Kay and Jin Akanishi, from the boyband KAT-TUN, wrote a duet together called “Wonder”. The song was first performed by Akanishi on the KAT-TUN’s concert tour in 2009. This was the second time that Crystal Kay sang with him, the first time being during her second appearance on KAT-TUN’s variety show, Cartoon KAT-TUN.

On August 12, 2009, Crystal Kay released her twenty-fourth single, “After Love (First Boyfriend)” / “Girlfriend”. The single was announced on Crystal Kay’s official website on July 1, 2009, which marks the tenth anniversary since the release of Crystal Kay’s debut single in 1999. “After Love (First Boyfriend)” features Kaname from the J-pop duo Chemistry. “After Love (First Boyfriend)” is a follow up to Crystal Kay’s 2003 single “Boyfriend (Part II)” and used as the CM song for Tully’s Coffee commercials throughout July 2009.

On September 2, 2009, Crystal Kay released her second compilation album, entitled Best of Crystal Kay. The collection featured over thirty tracks from her discography. Best of Crystal Kay was also released with a “limited edition” disc containing four new songs, including “Step by Step”, produced by Yasutaka Nakata of Capsule. It was used as the theme song for “Janguru Taitei” which aired from September 5, 2009. Another new song, entitled “Over and Over” will also be in the CD. It is currently used in a commercial for NTT’s “Live On FLET’S”. Crystal Kay did not star in this advert. “Over and Over” was produced by Taku Takahashi of M-Flo. The fourth track “Helpless Night” is a collaboration between Crystal Kay and Jin Akanishi of KAT-TUN and is performed almost entirely in English.

In 2009, Crystal Kay stated that “There is still some racial thing going on, [but] people are getting used to it. You can see a lot more mixed people on TV, and even (among) models in magazines.” At a summer festival that year half-Japanese half-Papua New Guinean singer Emi Maria left Crystal Kay a demo and a note saying “You’re my idol, I’m sad I couldn’t meet you in person.”

In 2010, Crystal Kay starred in her first role in a drama series. She played the character of Kokusho Akira, a genius hacker who has carried out many crimes all over the world in the Nippon Television drama Hidarime Tantei Eye, which stars Hey! Say! JUMP member Ryosuke Yamada. The drama began airing on January 23, 2010.

On April 29, 2011, Crystal Kay held a Q&A on her blog and answered her fans’ questions, with one question regarding a possible Korean debut. Considering her mother is of Korean ancestry, she has stated: “I can speak just a teeny bit of Korean (lol). My reading and writing are perfect, but learning vocabulary is sooo hard! It’s no good that I don’t do listening or speaking. I’ll think about a Korean debut! I’d like to be able to sing in Korean.”

On October 5, 2011, Universal Music Group subsidiary label Delicious Deli Records posted an announcement that after twelve years Crystal Kay had left Sony Music Japan and signed to them.

In 2012, Crystal Kay recorded a cover of “Eyes on Me” for the “FINAL FANTASY Orchestra Album”, becoming the latest in a series of notable artists to cover the song, including Angela Aki, MayBee and Kanon.

On February 14, 2014 she officially released her US debut music video via MTV Iggy, “Busy Doing Nothing”.

In 2019, she starred as “Leading Player” in the Japanese version of the Broadway musical Pippin, for which she was awarded by the 27th Yomiyuri Theater Awards as best actress.

In spring 2020, she will play the role of “Motormouth Maybelle” in the Japanese version of the musical Hairspray. On March 17, it was announced that Crystal Kay would release her first cover album in fall 2020. “March 9”, a beloved graduation song in Japan, was pre-released on March 18 as the first track of the album. On April 24, the musical Hairspray was cancelled due to COVID-19 pandemic in Japan.