Billie Eilish- "Blue"

"Blue" is the closing track on Billie's third studio album, "Hit Me Hard and Soft" that was released in May 17th, 2024.
"Blue" is a combination of two songs that Billie had previously written, "True Blue" and "Born Blue".
"True Blue" was one of the first songs she and Finneas had ever written at the age of 14, and was performed along with "Ocean Eyes" during some of her earliest performances, which later got leaked in 2022, while "Born Blue" was a song that they started writing for "Happier Than Ever," even putting it on an early version of the track list, but only wrote a few lines and never finished it.
The lyrics of the song contain references to another song on her album, "Birds of a Feather", which is thought to be about dating her ex Jesse Rutherford.
The song's melody is used as a motif throughout the album. There's been speculations about Billie making "Blue" just like "Goodbye". The song has so many layers.
The song ends with the line, "But when can I hear the next one?", leading to speculation about a sequel or sister project to "Hit Me Hard and Soft".