Ghosts and Glass
From Halopedia, the Halo wiki
Ghosts and Glass is the nineteenth track (Disc 2 Track 12) included in Halo: Reach Original Soundtrack.
The track opens with strings playing a short suspenseful melody, followed immediately by low strings taking the lead in a sad melody that is the first theme, ending with harp accompaniments. A solo flute then take over for the opening of the second theme, playing a mournful but hopeful melody, which is continued by strings. The track ends with a reprise of the first theme.
The ending of the second theme was adapted into the ending of the earlier track, Ashes.
The full piece is a bonus track found exclusively in the soundtrack, and thus cannot be heard in any part of Halo: Reach.
However, a shortened version of the first theme, featuring a more prominent low strings section, titled Return (from the earlier track The Package), plays in the opening cinematic of the campaign level The Package.