Organic Angel Alexiel, who is one of the highest and most powerful beings in existence, rebelled against God when, supposedly, she became disgusted by the way angels were behaving. She was captured and faced with the ultimate punishment of heaven, to have her soul reincarnated into human lives, and each of her lives would end tragically. The story follows her latest incarnation, Setsuna Mudo, who is romantically in love with his younger sister.
In this series Assiah (Earth) and the upper levels of Hell (Gehenna) are mirror images of each other. As mankind polluted and destroyed the Earth the lands of Hell also began to weaken. Taking advantage of their creator's sleep and the weakening of their enemies, the angels of heaven wage war on the Evil race (a group of beings that are demons who have turned away from the Devil, Lucifer, and God; they live in Gehenna and worship "Holy Dragon Gods"), wiping most of them out.
In doing this the angels fighting the war are corrupted. They commit vile crimes and murders under the name of God and righteousness. This deeply goes against Alexiel's morals. She feels that the Evils are more pure in their actions since they do not put up a charade of purity to cover their crimes.
