Starting with One, all of the sisters (including Zero) will have their extra DLC stories and battles released, starting next week Thursday, March 6th!!  Each sister’s DLC will be released separately every week for 600 yen.

It sounds as though each sister will also have a corresponding Weapon Story, too. Comparatively, as you level each sister up, it will unlock bits of their memory to better flesh-out their character and personality for the player. Hopefully this way, we can learn much more about them!!

Source: http://blog.livedoor.jp/od3/archives/52060778.html

Follow-up by Gematsu: 
http://gematsu.com/2014/02/drakengard-3-story-dlc-hits-japan-next-week