In the middle of the song, a woman’s voice says, “Goodbye, good night” and it has been revealed that the voice is none other than Girls’ Generation’s Yuri. A representative stated, “It’s a short part, but it has a pretty large impact. Yuri’s voice goes well with that portion of the song and thus, it was being inserted.”
“It was originally supposed to be melody only, but Max Changmin proposed to have a female voice for the narration. Composers and staff gathered to find the suitable voice for the part and they selected Yuri.”
Yuri’s voice could be heard at 1:39 mark.