The NieR "series" is basically a spin-off of Drakengard, based on a certain side-ending of Drakengard 3 if I remember it correctly. As none of the main Drakengard otherwise exists within the NieR universe nor do they have PC ports, I don't really think we need to name the series for Drakengard.
If one of those games eventually comes to PC as well, the NieR series would basically be a child series to the Drakengard series.
Do you agree? :)