Hanako Oku
Oku Hanako is a Japanese pop artist who uses her keyboard almost exclusively in her works. She mostly does piano ballads. She was signed to a major recording label in 2005. Born in Funabashii, Chiba on the 20th of March 1978. She’s played piano and trumpet, and has written lyrics and music for a good 17 years.
The theme song to the film 'Toki o Kakeru Shōjo' (The Girl Who Leapt Through Time) is "Garnet" (ガーネット, Gānetto), and the insert song used in the film is "Kawaranai Mono" (変わらないもの, lit.