Angel Sanctuary (天使禁猟区; Tenshi Kinryōku) is a highly controversial anime based off of the manga by Kaori Yuki. This 20-volumed manga serialized on Hakusensha 's Hana to Yume. Both the manga and anime feature mature content.

The manga is available in English, published by Viz Communications.

Story

Setsuna Mudō is a problematic delinquent high school student, who is in love with his sister. To add to his problems, he is also a reincarnation of a fallen angel, which gets him caught in a messy war between heaven and hell.

Angel Sanctuary is one of Kaori Yuki's most celebrated works. Among other things, it discusses the morality of incestuous relationships, the nature of God, and other deep and philosophical topics.

The background story is that of Organic Angel Alexiel, who is one of the third highest beings in existence. Being just under God himself and the primordial man known as Adam-Kadamon. She is, in rank, equal to her twin brother the Inorganic Angel Rociel. 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 Earth and the upper levels of Hell (called Gahenna) 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 creators slumbering absence and the weakening of their enemies the angels of heaven wage war on the demon race, wiping most of them out.

In doing this the angels fighting the war show themselves to be corrupt. Committing vile crimes and murders under the name of god and righteousness. This deeply goes against the morals of Alexiel. She states that demons are more pure in their actions since they do what they are made to do. In addition they do not put up a false charade of purity to cover their crimes. She joins the demon side of the war and declares an official battle against god, despite the fact that he has apparently been asleep and oblivious of this, having left other angels to take his place in ruling.

The war comes to a climax and end when Alexiel fights against her brother Rociel. Rather than killing him, something she was either unable or unwilling to do she attempts and succeeds in sealing him away within the earth under a barrier of forbidden magic. However in doing this her sword, the seven bladed sword of the spirit, breaks and strikes both her and Rociel. The result is that both Rociel and Alexiel are defeated. Rociel sealed away and Alexiel taken into Angel custody.

For her crimes Alexiel is sentenced to one of the most horrid things the angels can think of. Her body and Soul are separated. The body is frozen into an angel crystal, it is then locked away in the deepest depths of angel security. Her soul is sentenced to be incarnated into a human mortal. That mortal’s life is sentenced to end in a violent and painful way. After which Alexiel is re-incarnated again and begins the cycle anew. However in reality it seems that she does not so much inhabit the mortal as ride along. She is like a passenger in the body of another mortal. The body also contains the soul of its true owner who controls it. She has little or no influence over the body, however her mere presence causes the mortal to have strange spiritual patterns and powers. In present time she is incarnated into a boy named Setsuna Mudō.