Truth Seeker Devianne:
It is to retrieve the Atelia extracted by the demons that has not turned into Dark Atelia yet.
Extracted Atelia cannot be retrieved because it is sent to a special device automatically, but we can still get it mid-extraction.
Atelia in Extraction can be retrieved from Death Rogue, Death Shooter, Death Warrior, Death Sorcerer, Death Pondus, Devil Nightmare, Devil Warrior, Devil Guardian, Devil Sinist, Devil Varos, Demonic Wizard, Demonic Warrior, Demonic Archer, Demonic Keras and Demonic Weiss.

Retrieving Atelia will eventually stop Etis van Etina from getting more Dark Atelia so it's ultimalety weaken the force of Embryos.