Angel Sanctuary by Kaori Yuki Manga Manga Manga!

Angel Sanctuary is about a boy, Mudou Setsuna, who is the reincarnation of a fallen female angel, Alexiel, condemned by God to die a painful death in each incarnation; in his present life, he is in love with his blood sister, Sara, but besides this problem, he becomes the focus of a war between angels and demons and must save humanity from destruction.