User blog comment:Omega natsu2/Chapter 360: The White Inheritance, Predictions./@comment-24066070-20131108151629

White Legacy may be something used by the Council to seal demons, like Lullaby, therefore Tartarus wants it to undo the seals on Lullaby and some other unintroduced demons. This may explain why Michelio immediately thought of something they may be after.

These demons may be used to strengthen E.N.D. or the NDG (absorbing their power or something along these lines) or simply serve as footsoldiers.