Drakengard 3 will be supported with DLC set before the events of the main story, allowing players to take control of Zero's sisters.
Drawing on Japanese reports from the latest issue of Dengeki, Siliconera reports the prequel DLC will offer the chance to play as each of Zero's five sisters (whose names are One through Five).
It's not clear whether this piece of DLC, which is not yet available in Japan, is the one Square Enix will ship with the boxed special edition coming to North America; that DLC is known to make One playable, so it may be the same thing.
Drakengard 3 is itself a prequel to the other two games in the series (and is related somehow to spin-off Nier). It tells the story of six magical Intoner sisters, who descended from the heavens to bring peace to the land. Zero has rebelled against the group and determined to kill them - although officially we don't yet know why. As with previous Drakengard games, gameplay is divided between hack-and-slash action and aerial combat on dragons.