In the Japanese version's commentary with the game's composer Masaharu Iwata, he stated that the theme for "Unavoidable Battle" was the first battle theme he created. Before "Unavoidable Battle", he created another battle theme before it, but it felt too happy-sounding, so the team rejected it. As he reflected on it, he created "Unavoidable Battle" to be a more pointed, exaggerated song, while the rejected music was re-purposed and used for the Unit Introduction theme, which is played over the opening demo.
Contributed by ProtoSnake