Outside of the opening and closing title music, Memory is perhaps the most fundamental theme of Cowboy Bebop. Not only is it the very first piece of music heard in the show, being used in the cold open of Session 1, Asteroid Blues, it re-occurs frequently, often being used during important moments of introspection, typically involving either Spike or Faye.
The only released version, the track officially titled Memory, is used exclusively when referring to Spike's past. In this form, the melody is distilled down to just that of a simple music box.
As well as the preview for Ballad of Fallen Angels, it also re-occurs when Spike is re-united with Julia in the graveyard at the end of The Real Folk Blues (Part 1), and is reprised as that scene continues at the start of Part 2, which means Memory is also the only song used in the only cold opens of the entire series.
Piano Bar II
The more frequently used version of Memory is commonly known as Piano Bar II, a lounge jazz piano interpretation which remains unreleased. It is often used to underpin moments involving Faye, but its first occurrence is in Jamming With Edward during the news broadcast about Mpu (although thematically this still makes sense, with both Mpu and Faye being who they are in the present is as a result of the Moon Gate explosion in the past).
In Jupiter Jazz (Part 1) Piano Bar II forms the backdrop for Faye meeting Gren at the Blue Crow, and is also used for the preview for Jupiter Jazz (Part 2). It is used in the preview for My Funny Valentine, and then in that episode when Faye first talks to Whitney from her hospital bed. Its last major appearance is during Cowboy Funk, being played while Faye visits Andy on his boat; a short callback to it is, however, used to accompany the Session Title card in Hard Luck Woman.
It's currently unclear if only a single recording of the piano version was produced, or if multiple performances were made as needed, timed to fit particular scenes: in Jamming with Edward, however, it clearly didn't as there's an obvious cut made to the song in order to fit in the flourish at the end before cutting to the next scene.
- As if to reinforce just how significant this song is to Cowboy Bebop, the theme from Memory is also an important phrase in the vocal melody for Adieu, first occurring in the second verse: "Don't care for me, don't cry / Let's say goodbye, Adieu / It's time to say goodbye").