In the Fifth Generation, more and more souls are being born with so-called "weakness marks." To the system, these children appear sick: their bodies may be fragile, and their minds overly sensitive to crowd noise and city bustle. But the Guardians know the truth.

This is not an illness—it is a Fine Tuning.

Their souls are so great and bright that the coarse matter of this world can barely withstand their energy.

They are living lie detectors. Where an ordinary person might ignore falsehood, a "different" child will feel physical pain. The Creator deliberately sent such souls into the Fifth Generation to become living filters, purifying the world of the poison of past eras. They are the Hunters' primary target, but also the Guardians' primary concern.