[4] Sun Dance and Penny Rain were Aimer's first new studio albums since daydream in 2016.

[7] In February 2018, Aimer thought about a concept for her next album after releasing her single "Ref:rain".

She then came up with the concept of "Sun and Rain" and used it for her "soleil et pluie" Hall Tour from October 2018 to January 2019.

The development of Sun Dance began with the song "3min", which was first performed live on Aimer's Fan Club Tour in August 2018.

In addition, after first performing "ONE" live at her Nippon Budokan show in 2017, she desired to record a more upbeat album in contrast to her darker themed releases.