Several years after the end of Bubblegum Crisis, things have calmed down, or so it seems. Sylia's disappeared, Priss has stumbled from one manager to another, Nene's still working with the AD Police and trying to keep the Knight Saber ideal alive, and Linna has moved into the Stock market and is doing quite well. Things are quiet, until a group of mercenaries calling themselves the Illegal Army begins to attack high tech companies, stealing rare parts. Sylia returns with new hardware to reform the Knight Sabers, but will they be able to take on the Illegal Army, and whoever is behind them?

Enslaved by an army of rebellious super robots originally designed to help civilization avert a complete ecological cataclysm, mankind's only hope is Casshan, a legendary hero who wages a solitary war to defeat the NEOROIDS and restore the Earth to its rightful order. Ironically, Casshan's father is the same scientist who engineered the race of super androids now threatening to destroy all of mankind.