Okai Chisato first joined Hello! Project in 2002 as one of the fifteen children chosen from the Hello! Project Kids auditions. In 2004 Berryz Koubou was formed, with the intention of rotating the kids throughout the unit. Okai didn't make the original pick, and the idea was eventually dropped.
The remaining kids ending up forming °C-ute in 2005. The group didn't make its official debut until late in 2006, with their first official single released in February 2007.
She was a member of Little Gatas until she was added to Gatas Brilhantes H.P.. She was also a part of the unit Athena & Robikerottsu consisting of Okai, Niigaki Risa, Mitsui Aika, and Nakajima Saki, in 2007. They sang the opening and ending theme song for the anime Robby & Kerobby.
She was put in Tanpopo with Kamei Eri, Mitsui Aika, from Morning Musume and Kumai Yurina from Berryz Koubou
A video of was uploaded to ℃-ute's Official Youtube Channel, called "Dance de Bakoon! dance cover - Okai Chisato (the person herself)". It achieved 100,000 views in 2 days; upon reaching 500,000 views, ℃-ute's new single "Aitai Lonely Christmas " PV was released in celebration. Along with a new photobook and DVD, she will now become the first member of C-ute to get her own single and a separate listing on iTunes. The release date is Nov 27, 2010, and price is 200 JPY or 1 USD. Before the year ended, She released 2 more songs on itunes.
Another song was released on itunes by her on Jan 24, 2011. So far she has a total of 4 solo songs under her itunes. (Love Namidairo, Romantic Ukare Mode, Manatsu no Kousen and Egao ni Namida ~THANK YOU! DEAR MY FRIENDS~). Okai also had a solo DVD/CD come out called Solo Live 2011 Vol.1 ~Kaisha de Odotte Mita!~. The CD contains 2 songs from her Itunes, while the DVD has singing and dancing of 12 songs. (Some songs just the dance alone). With the new release of C-ute's new single Kiss me Aishiteru, she is one of leads. This would make it her first time leading a single.