In 2004, Oku began to perform on the streets of Tokyo, mainly in Shibuya ward, but once sold 402 CDs in four hours outside Kashiwa railway station.

In April 2006, the animated film The Girl Who Leapt Through Time was released, with the theme songs "Garnet" and "Kawaranai Mono" sung by Oku.

Lemon Hall, and with the release of her album Time Note, she once again performed sold-out concerts there over three nights in July 2007.

[4] In 2010, Oku began hosting a new radio show E-Tracks Selection once a fortnight on FM OSAKA.

[5] An animated music clip of the album version of Oku's song "Kimi no Egao" was released, through Pony Canyon's official YouTube channel, on May 7, 2017.