 On May 2, 2018, Starship Entertainment and Fantagio collaborated to form a special four-member unit named WJMK, consisting of members of their respective girl groups Cosmic Girls and Weki Meki.Choi and Kim, together with Seola and Luda of Cosmic Girls, released the single "Strong" on June 1, 2018, along with its accompanying music video.Kim was part of the cast of "Shoot-out Mart War" alongside Cha Eun-woo, Park Soo-ah and many more.