"Eternity" was written by lyricist Kim Eana, who also wrote VIXX's last four title tracks.

The song's lyrics portray the fantasy of time, and is about the miracle of love that exists in the moment and forever.

On May 18, VIXX announced that they would be coming back with their fourth single album "Eternity" through a post on their official fancafe.

"[5] "VIXX's 4th single album concept is a 'time fantasy' and expresses the miraculous love story that happens in the present and for eternity."

The second track "Sad Ending" was composed and arranged by Swedish producers Erik Lidbom and Jon Hallgren, with lyrics written by Lee Seu Lan of Jam Factory and Ravi.