It starts with the typical life of Setsuna: Rejected by his mother, in love with his sister, getting into fights, but faints the MOMENT he sees blood. Kira Sakuya, Setsuna's sempai helped him in his life countless times, always cheering him up and being there when he needed him. Who was actually the spirit of Nanatsusaya.
Setsuna's classmates starts talking about a computer game called: Angel Sanctuary. Which was Katan's (He is the "son" of Rosiel, he was once a Grigori who had no sense nor body. Rosiel created a body for him and named him Katan. Katan worked his way up to the top layer of heaven in order to be close to Rosiel because he was grateful of what Rosiel did and decided to follow him. Katan eventually became a Cherubim, a member of one of the highest ranks of angels.) doing for trying to reawaken Rosiel. In the game, Rosiel can talk to them and will fulfil their wishes if they help him. Soon afterwards, Sara's best friend Ruri somehow gets the CD-rom and began playing the game. The reason why she was so into this game was because she was in love with Setsuna, and the CD offered her beauty and that once Set-chan sees Ruri, he will fall in love with her immediately.
At the same time, 2 demons from hell named Kurai and Arakune came to Earth in search for the soul of Alexiel in order to lead another rebellion against heaven. Kurai was also the princess of Anagura, the leader of the race of Evils, who has stolen the crystal which preserved the body of Alexiel and has taken it to her castle to look after her. (Kurai's obssessed with Alexiel, as you can see... ~.~)
Rosiel talks to Ruri in the computer game and convinced her to give up her body, she does, and Rosiel enters the body of Ruri.
Kurai and Arakune confronts Setsuna with the story of him being the reincarnation of Alexiel, but Setsuna refuses to believe them. Disguised as Ruri, Rosiel kidnaps Sara to lure Setsuna into a warehouse, where he hass a ghoul he made out of one of Kira's juvenile friend to attack Setsuna. Setsuna is almost killed, but then a vision of Adam Kadmon appears and heals him. Rosiel cannot stand the radiance of Adam Kadmon and is about to be destroyed when Katan creates a magical pathway and pulls him into safety.
Disguised as Ruri again, Rosiel goes to Sara's house and collects data from her while she was asleep to which he can transform into Sara.
Rosiel transforms himself into Sara and asks Setsuna for a kiss. The reason for that was to make Setsuna one of his dummies by feeding him one of his feathers, in the form of a pill. The pill, of course, was in his mouth. Just before kissing Sara, Setsuna suddenly realised that the fragrance of Sara was wrong. So he stopped and asked Sara/Rosiel who she really is. Rosiel told him, and Setsuna was in shock. Katou took a picture of Sara and Setsuna almost kissing and posted it all over the school. By the way, Katou has been taken over by Rosiel as well. Setsuna, suddenly enraged, pulled out the sword, which Kira had given him in the form of an earring, and slashes katou. But Rosiel left katou's body just in time. Then kira tells Setsuna about himself, that he's only being nice to Setsuna because he is the soul of Alexiel that he only cared about Alexiel. So, Setsuna ran away, feeling hurt, upset and betrayed. But kurai explained Setsuna that Kira did care about him. And that was why he had stayed in one body for so long- he began to have human emotions (no, he's not gay) towards Setsuna.
Sara's mother, Mrs. Mudou decides to go to England where she can find a husband for Sara. Sara agrees because she knows that Setsuna and her will never find happiness. She never told Setsuna she was leaving. Kurai knew and told him to go to the airport and come back with her. Setsuna does so and begged Sara to stay, Sara does. They decided to run away together.
Some kid finds the body of katou buried in the mud and called the police. They believed that Setsuna was the killer, and went after him. They stopped Setsuna and were about to arrest him when Kira admitted that he killed Katou.
Setsuna and Sara made love in a hotel and came back because they couldn't bare the thought that their friend was in jail because of them.
At the train station, Kirie tricks them into a construction place and Kirie attacks Setsuna who is off his guard, but Sara jumps in front of him taking the hit that was meant for him and dies. Setsuna, in this time of grief releases his powers to destroy the world.
Adam kadamon came and stopped time on earth, naming setsuna as the Messiah and told him to go to the tower of Etemenaki to release him. But setsuna wants to have Sara alive again. And the only way to do so is to retrieve Sara's soul from Hades.
I will continue to write more and more on this, but geez this is way too bloody long. There are 20 volumes to the manga and each have about 6 chapters. There is so much detail that you just want to continue reading and not stop. My suggestion is go out and buy the manga and watch the OVA, you will not be at all disappointed and is well worth the money.
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