​Six years ago, Riselia lost her home and family during the Void Stampede that destroyed the Third Assault Garden. Only she
and Regina were thought to have survived, yet the floating city has mysteriously reappeared--and it's broadcasting a distress signal. Leonis and the girls of the eighteenth platoon are sent to investigate, but they end up stumbling into a situation far more perilous than they expected. Even the power of the greatest Dark Lord may not be enough to save them this time!