Conversation so far:
Who has Kim Jae-joong collaborated with?
Kim Jae-joong collaborated with label-mates The Grace for the Japanese version of their song Just for One Day“.
Has Kim Jae-joong had any other collaborations besides with label-mates The Grace for the Japanese version of their song Just for One Day“?
On 30 September 2009, Kim Jae-joong and bandmate Park Yoo-chun released a self-composed single Colors (Melody and Harmony)/Shelter.“
Did Kim Jae-joong work a lot with Yoochun?
Kim Jae-joong and Park Yoo-chun also participated in m-flo's album m-flo TRIBUTE -maison de m-flo, singing the track Been So Long.

Question: What soundtracks did he work on?
Self-contained rewrite: What soundtracks did Kim Jae-joong work on?