[9] In his adolescence, he enrolled at an academy for lessons and attended a private audition held by YG Entertainment through the facility; as a result, Choi was successfully recruited in its trainee program in 2015.

[13] Choi was also incorporated in the third episode of YG Future Strategy Office (2018) as himself that same year while filmed alongside other trainees from the agency.

20-year-old Choi (Korean age) competed in YG Treasure Box (2018–2019), a survival reality program composed of twenty nine trainees, as one of seven under "Team A".

[18] In the midst of its preparation for debut, Choi featured on the B-side single, "1, 2" (한두번; handubeon) by label-mate Lee Hi from her extended play titled 24°C and participated as its lyricist.

[15] In January 2018, Choi modeled for Japanese sports clothing and accessories brand, Descente, for their new semester menswear range.