From the dawn of time, the planet Eden's angels have been diligently observing the actions of its inhabitants - known as "Earthians". Chihaya and Kagetsuya, representatives from Eden, were assigned to evaluate both the advantageous and disadvantageous traits of Earthians. Despite the guidelines Chihaya was given, he often gets caught up in Earthian affairs, much to Kagetsuya's displeasure. As Chihaya unravels the mystery surrounding his unusual black wings, he uncovers secrets one after another.