User blog comment:ChishioKunrin/Instances of Leit Motifs in Volumes 1 & 2/@comment-18396318-20150605182352/@comment-25555436-20150605224915

Actually, TWBTD works as Ruby's theme. Hell, it works more than RLR does. Just read the lyrics, they fit her almost-perfectly.

Plus, in any case, TWBTD was Volume 1's opening song, the main theme. And TTSG was the same for Vol.2. It's very, very common in fiction to include a part of the main theme in a certain part of the soundtrack or two, only with a different musical arragement.

Halo is particularly guilty of this. The "Halo Theme" appears in nearly every one of the games's soundtracks. Not as the actual theme, unless you count Halo 2's remix of it. But instead, as a small appearance or addition during certain parts of certain songs.

One example: The Halo theme appears in Halo 3's appears briefly in Finish the Fight, at around the 1:23 mark, but with a somewhat-different arrangement.