Creative director Yoko Taro cites the novel Hybrid Child by Ohara Mariko as a source of inspiration for the Nier portion of the series.
The Drakengard 10th Anniversary -World Inside- material book contains a gag ad for "Drag-On Dragoon 4". The ad features art done by Kimihiko Fujisaka, concept artist for the Drakengard series.
Each of the games take place on there own timeline, rather than being direct prequels/sequels.
In Japan, the series is known as Drag-On Dragoon. The name was changed to Drakengard during localization.
Dragons and Divine Beasts are usually named after biblical angels while human characters are named after demons.