Tanaka auditioned for a spot in Morning Musume's 5th Generation in 2001 and passed, but had to leave the training camp when it was found that she was underage. She attempted again in 2002 for a position in the 6th Generation and passed along with members Eri Kamei and Sayumi Michishige, making Tanaka the only member who auditioned twice to get in. She provided the main vocals for the single Shabondama. She was featured in two solo versions of Memory Seishun no Hikari on a fan club release CD.
In 2003, Tanaka was chosen as a member of new unit Aa!, along with Miyabi Natsuyaki and Airi Suzuki, two Hello! Project Kids. They released one single, "First Kiss", before going on an indefinite hiatus. The group reformed in 2009, only this time without Tanaka, as she was already in the group High-King. Her place in the group was instead taken by Hello! Pro Egg member Akari Saho.
On March 28, 2008, it was announced that Tanaka would be taking on the voice acting role of Kirara, a main character in Sanrio's anime Onegai My Melody Kirara, the fourth My Melody series. The show premiered on April 6, 2008.
In 2008, Tanaka became the leader of Hello Project's new unit High-King.
It was revealed in late 2009 that Tanaka would be voicing the main/title character of the new anime series, Kaitō Reinya ("Phantom Thief Reinya"). The main character, Reinya, had initially been modeled on Tanaka. The show began airing on January 8, 2010.
On 18 November, Tanaka announced that she would graduate from Morning Musume at the end of the 2013 Spring Tour.