Kim collaborated with fellow BTS member V on the song “It’s Definitely You”, released as part of the Hwarang: The Poet Warrior Youth original soundtrack. He also joined BTS member Jungkook to sing and release an alternate version of “So Far Away”, a song from BTS member Suga’s self-titled mixtape Agust D. Kim’s solo covers include “Mom” by Ra.D, “I Love You” by Mate, and “In Front Of The Post Office In Autumn”, originally by Yoon Do-hyun in 1994. They were released on SoundCloud on May 7, 2015, December 3, 2015, and June 7, 2018, respectively. He has also made several appearances as a co-host for Korean music award shows, such as Music Bank and Inkigayo.
On June 4, 2019, Kim released his first independent song “Tonight” as part of the 2019 BTS Festa, a yearly event celebrating the anniversary of the band’s debut. The acoustic ballad was composed by Kim, alongside Big Hit Entertainment record producers Slow Rabbit and Hiss Noise. The lyrics, written by Kim and BTS leader RM, are inspired by Kim’s relationship with his pets. The track was met with generally positive reception, with praise directed towards Kim’s vocals and the song’s calming atmosphere.