[6] Prior to debuting professionally, Kōki had written three songs for her mother Shizuka Kudo's album, Rin, in 2017,[4] as well as for Mika Nakashima.

[3] In May 2018, Koki debuted as a model, appearing in the July 2018 issue of Elle Japon.

[7] Kōki has also appeared on covers for fashion magazines such as Numéro Tokyo,[8] Grazia China,[9] Nylon Japan,[10] and Vivi.

[12] In October 2018, Kōki appeared in her first commercial, endorsing products from Otsuka Pharmaceutical.

[15] Kōki made her runway debut at the 2019 Paris Fashion Week, representing Chanel.