Twenty-three years ago, miners in the Yamnask Empire began to discover strange and immense humanoid machines buried deep beneath the earth.

The secret to harnessing their awesome power? Music—horrible, alien song unlike any known to human ears. Fervent study of these machines by the newly-formed Eternal Choir ushered in an era of great prosperity and technological progress for the country, but the rest of the world was not about to sit idly by.

Now, the Eternal Choir wields their army of mechanical dolls in unending conflict to defend Yamnask against those who want them for themselves. An award-winning vocalist, Milaslava Cheplieva, was chosen to lead a chorus of elite pilots and see her country to victory.

But as she learns more about her teammates and the mysterious machines they pilot, will she be able to bear what she must do and who she must become?