Jang Kyu-jin was born on May 26, 2006—sharing her birthday with ITZY's Yeji. She trained at WithBill Dance Academy before joining JYP Entertainment through a private audition. During her training period, she appeared at JYP's trainee showcases, building recognition among K-pop fans well before debut.

On August 6, 2021, Kyujin was revealed as the third member of JYP's new girl group through a dance performance video alongside Jiwoo and Jinni.1 The reveal was part of an unprecedented marketing campaign where JYP offered a "Blind Package" pre-order for the group's debut album without revealing the members or music. The limited edition package recorded 61,667 pre-orders during its brief sales period.1

NMIXX debuted on February 22, 2022, with the single album "Ad Mare." At just 15 years old and still in middle school, Kyujin took the center position for the experimental title track "O.O."2 At the debut press conference, she described hearing the song for the first time: "I felt as if I was in a completely different world. As the melody and rhythm of the song continuously changes through the music, I thought 'O.O' would be the perfect song that could leave a bold mark in people's minds."2

The debut made history: "AD MARE" sold over 227,000 copies in its first week, the highest first-week sales of a debut single by any girl group at that time. The record was later broken by Le Sserafim in May and NewJeans in August of the same year.3

Kyujin's youthful appearance—with doll-like features, fair skin, and round sparkling eyes—captured attention across Korean online communities. Fans drew comparisons to Oh My Girl's Hyojung and gave her the title "Next Visual Queen of Gen Z K-pop."4 Her combination of dance skills and visual appeal made her what the K-pop community calls a "stan attractor"—someone who naturally draws people to become fans.4