[2] Yu Aoi made her stage debut as Polly in the 1999 rendition of Annie, followed by her appearance as a regular on TV Tokyo's Oha Suta (The Super Kids Station) in 2000.

A year later, she debuted in Shunji Iwai's All About Lily Chou-Chou playing Shiori Tsuda alongside Hayato Ichihara, Shugo Oshinari, Miwako Ichikawa, and Ayumi Ito.

She also had supporting roles in the Satoshi Miki film Turtles Swim Faster than Expected starring Juri Ueno, and Yamato with Shido Nakamura and Kenichi Matsuyama.

Aoi also lent her voice to play Shiro in the animated film Tekkon Kinkreet, the adaptation to the Taiyō Matsumoto manga, Black and White, directed by Michael Arias.

In 2007, she participated in the live-action adaptation of the manga series Mushishi alongside Joe Odagiri, as well as WOWOW's Don't Laugh at My Romance, Welcome to the Quiet Room with Yuki Uchida, and going back to the stage to play Desdemona in a rendition of Shakespeare's Othello.

[citation needed] Aoi began 2008 with the release of Don't Laugh at My Romance, which earned her a nomination as Best Supporting Actress at the Asian Film Awards 2009.

A couple of months later, NTV signed Aoi to play her first TV leading role as Handa Sen in the live-action adaptation of Shota Kikuchi's manga series Osen, which aired until the end of June with ten episodes.