It's one of the best manga I ever read heart
the story is :
The background story is that of Organic Angel Alexiel, who is one of the highest beings in existence, third only to God himself and the primordial man known as Adam Kadmon. Alexiel is equal in rank to her twin brother, the Inorganic Angel Rosiel. Before the beginning of the series God has fallen asleep to "gather his powers" which indicates that he is, in this series, very powerful but not omnipotent.
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" wink , 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. She joins the Evils' side of the war and declares an official revolt against God.
The war comes to a climax and end when Alexiel fights against her brother Rosiel. Earlier, Rosiel had found out that he is decomposing and that his mind will rot. He went to Alexiel to ask her to kill him before he goes crazy, which she agrees to. But when she is about to deal the killing blow to him, he yells "Would you kill your own twin brother, Alexiel!?". She then is filled with pity and remorse, so she seals him within the Earth using a barrier of forbidden magic. However in doing this she used every ounce of her power and shatters Nanatsusaya (the "Holy Sword of God", that made every bearer before Alexiel go mad with its power and kill themselves and countless others). The result is that Rosiel is now sealed inside Assiah and Alexiel is captured and tried by the Angel of Judgment, Uriel.
For her crimes, Alexiel is sentenced to the most severe punishment given to the fallen. Her body and soul are separated. The body is frozen in an angel crystal and then locked away in the deepest depths of angel security on the fourth circle/layer of Heaven, Machonon. Her soul is sentenced to be incarnated into a human mortal. That mortal's life is sentenced to be filled with physical and emotional pain. Everytime Alexiel is re-incarnated, the cycle begins anew. But in every incarnation Alexiel's personality is still present under specific (e.g. dangerous) circumstances, which causes her incarnation to have strange spiritual patterns and powers at times; it is as if the incarnation has a multiple personality disorder. In the storyline she is incarnated into a boy named Setsuna Mudo.
Setsuna Mudo is a problematic delinquent high school student, who is in love with his sister (thus producing the emotional pain required by her punishment). To add to his problems, he is also discovered as the reincarnation of a fallen angel, which gets him caught in the complex war between heaven and hell.
