"Good-bye Days" (stylized as "Good-bye days") is a 2006 song by Japanese singer Yui, credited as Yui for Kaoru Amane.

The song was released as Yui's fifth single on 14 June 2006 under Sony Records.

The single's B-side, "Skyline", was also featured in the film as an insert song.

"It's Happy Line" is actually the title track of her first single, which was an indie release.

All tracks are written by Yui