South Korean singer Jeon Hee-jin, known mononymously as Heejin, was born on October 19, 2000, in Daejeon, South Korea. On September 26, 2016, Blockberry Creative announced Heejin as the inaugural member of the upcoming girl group Loona, releasing her self-titled single album, featuring the track "Vivid," on October 5 as part of the group’s pre-debut strategy. On February 14, 2017, Heejin made her debut in Loona's first sub-unit, Loona 1/3, alongside members Haseul, Hyunjin, and Vivi. Their debut mini-album, Love & Live, was released on March 13 and in October, Heejin, along with Haseul and Hyunjin, auditioned for the survival reality show Mix Nine, successfully passing the audition and finishing fourth among the female participants. In 2022, Heejin released the non-album single "Honestly" and collaborated with Loona member Jinsoul on "Masquerade," featured in the soundtrack of the television series Tracer. On March 17, 2023, she entered an exclusive contract with Modhaus, releasing "Algorithm" ahead of her debut extended play, K, on October 31, 2023, which reached number 14 on the Korean charts and 11 on the Billboard Top 100 K-pop Albums chart.