She was unable to speak Danish when her family first moved, and was bullied at school due to her and her brother being the only mixed race students.

The duo performed at the Roskilde Festival in 2015 and released a string of singles through Danish record label Forbandet Ungdom before eventually disbanding.

[16] In March 2021, de Casier released her second single from Sensational, "Drama",[17] which Pitchfork named among the best songs of the year.

[20] Music videos released for the last three singles and "Someone to Chill with" starred De Casier as her alter ego Bianka, a self-assured woman.

[27] "E-Motions", her single with British record producer Mura Masa from his 2022 studio album, Demon Time, was released in September 2022.

[28] De Casier co-wrote several songs for K-pop girl group NewJeans's second EP, Get Up (2023), including the singles "Super Shy" and "Cool With You".

De Casier said in an interview with GQ that it was her first time writing music for other artists, a process that she found "freeing".

The EP and its singles were commercially successful and critically acclaimed;[29][30] "Super Shy" was named among the best songs of the year by numerous publication, entering the top 10 in lists compiled by The Guardian, NME, Rolling Stone, and Pitchfork, among others.

[38] She has cited Sade and Destiny's Child as groups that shaped her sound, while stating that Portishead, Tricky, and Mariah Carey influenced her vocals.