At the age of 17, she was chosen from 3,000 girls to be the heroine of the Fall 2001 Fuji TV drama Kizudarake no Love Song (傷だらけのラブソング Tainted Love Song?). In November, she made her debut with Sony Music Associated Records with the single "Stars," which was also the theme song of the drama. The single would go on to become her best-selling single. Her second single "Crescent Moon", an 80s themed song, was limited to 100,000 copies. It sold out the first day of its release. In March 2002 she released her third single, "One Survive," and her first video collection, "Film Lotus". This was followed in May by her 4th single, "Helpless Rain", and in August, by her 5th single "Will", which went on to rack up sales of over 140,000. Both were top ten hits and sold around 100,000 copies, proving Nakashima's rising star appeal.
Nakashima's first album, True, released in August 2002, was a number 1 hit on the Oricon charts. The album boasted a mature mixture of jazz and adult contemporary pop. In 3 weeks, True sold a million copies, and has sold nearly 1,174,000 copies to date. Then, as a commemoration of one year since her debut, Nakashima released a Premium EP: Resistance, which hit the charts' number 1 spot for two weeks in a row. On December 18, a documentary video, Kiseki: The Document of a Star, was released. In 2002, the singer received the "New Artist of the Year" award at the Japan Gold Disc Awards and "Best New Artist of the Year" at the All Japan Request Awards 2002. She also won the "New Artist of the Year" award from the 44th Japan Record Awards.
Nakashima's second album, Love, which was released in November 2003, sold nearly 1.45 million copies, surpassing that of her debut. The Japan Composers Association awarded Love the Best Album Award. After releasing a second mini-album, Oborozukiyo: Inori, in September 2004, Nakashima topped the Oricon Album Chart again with Music in March 2005, as well as with her first greatest hits album Best in December of that year. Best is the third album by Nakashima to have sold a million copies or more, but like her second album, Best also outsold True in sales - by nearly 30,000 copies.
Her most popular songs include "Stars", Gundam Seed's ending song "Find the Way", "Sakurairo Mau Koro", and "Yuki no Hana", which was covered by South Korean male singer Park Hyo Shin and this covered song was inserted in the popular Korean drama I'm Sorry, I Love You. Another Korean version was sung by female singer Seo Young Eun. It was also one of the most popular karaoke songs in Japan in 2004. The song was first covered by Singapore singer Joi Chua in 2005 by the same title "Sorry I Love You". It was also covered by Mainland Chinese singer Han Xue on August 2004 in Mandarin; and by Hong Kong singer Vincy Chan in 2006, in Cantonese. An English version of Hana no Yuki was covered by Eric Martin (Mr.Big's vocalist) and featured in his solo album Mr.Vocalist 2008 which was produced and released in Japan. New Zealand soprano Hayley Westenra also covered the song in English as part of her 2008 album Hayley sings Japanese Songs which debuted at number 12 on the Japanese Albums Chart but broke into the Top 10 in its second week of release. Another covered version was released on June 2006, sung by Japanese male singer Hideaki Tokunaga. "Find the Way" was covered by Korean singer Bada (former member of kpop legend SES). In 2004 she sang the ending theme of the anime series based on the manga Hi no Tori as aired on