The song plays when the game starts, and plays along the opening movie. A part of this song also plays during the songs "Vanishing World" and "The Place We Should Return To".
Within the original soundtrack, there are two versions of the "Main Theme": the "GAME BOY ADVANCE Original Version" and the "Full Sound Version". The former is the first track of the first disc, while the latter is the orchestral version and the first track of the second disc.
"Main Theme" is the arrangement of the Tactics Advance theme, played during the title screen. It is also the first track of the original soundtrack. The track employs a number of string instruments.
The Tactics A2 version of this song plays on the title screen.