Translation of the song he uploaded to Changba. And according to the good sis eddytws' research, That particular song came from an album with a title that was referenced in the fiction. The same title was talked about by Johnny and ZZ in one of the BTS. Johnny seem to always upload a cover of sad songs whenever ZZ is out of the country. The first cover he did was when ZZ was in Korea while he JY was filming Demon Grl (he must have felt so overwhelmed and lonely working with new people and environment) and now ZZ is in Japan.
Slay king! 
