[3] In 2013, Yujin collaborated with then-Cube artist and Beast member Yang Yo-seob in "Perfume" which was released on April 30 as part of Cube Entertainment's first "Voice Project".

[5] In 2015, the quintet did a voluntary street busking performances to help children with developmental disabilities, attracting attention as a warm 'Hongdae idol' as part of their pre-debut activities.

[2][6] They released a self-composed song "You're My Love" (Korean: 유어 마이 러브) on March 13, 2013, through the online music site Melon and the official YouTube channel.

[7] On March 13, 2015, Cube Entertainment released the profile information and images of Yujin as the fourth member of CLC following Yeeun, Sorn, and Seungyeon, through their official social media.

[8][9] Yujin made her debut as a member of CLC on May 19, 2015, with the release of the single "Pepe" off the five-track EP First Love, of which all the proceeds were donated to children with developmental disabilities.

[10] On August 17, 2015, she joined the cast of Real Man for the third season's female soldier special as the youngest member among the ten entertainers including rapper Jessi, Japanese broadcaster Sayuri Fujita and former national tennis player Jeon Mi-ra.

[18] At the end of the year, Yujin shared a stage with cast member Jessi and Kim Hyun-sook performing S.E.S' "I'm Your Girl" at the 2015 MBC Entertainment Awards.