[Angel at Dusk Original Soundtrack] 26-dusk-select-02 

"The most important thing in prolonging the existence of this angel world was to remain [Unchanging]. It was permissible to use existing ability to adapt to one's own environment, but mutation was synonymous with destruction. Homogeneity was the source of unity, and would bring about everlasting stability. The genes of living things are easily destroyed by exposure to radiation. In mankind's effort to streamline their function for self error correction, they made it so that angels all shared the same DNA. All angels across the Earth became as one single life entity. From the skies to the depths of the oceans, there was an abundance of lifeless angels too, as any angels that experienced genetic variation were corrected. These lifeless angels were not living things, but more resemblant of [Material] as they required no energy to sustain their existence. Only contact with another living angel could fill their angelic cells with life and make them become active again. After their bad genes had been identified and corrected, living angels would expend a quantity of their own body to reproduce themselves through them. Based on the fear that this act could result in illness, mankind created a safety device to ensure the safety of the angel world."