Angel Sanctuary

Is a fantasy shōjo manga series written and illustrated by Kaori Yuki. It focuses on Setsuna Mudo, a teenager who learns that he is the reincarnation of an angel who rebelled against Heaven. After the death of his sister, he travels through Hell and Heaven to reunite with her.

Plot
Beginning in late twentieth-century Japan, Angel Sanctuary focuses on Setsuna Mudo, a 16-year-old troubled high-school student who is in love with his 15-year-old sister Sara. While struggling with his incestuous feelings for his sister, he learns that he is the reincarnation of Organic Angel Alexiel, who led a rebellion against her fellow angels after witnessing their slaughter of the Evils, a group of demons, after God's disappearance. At the conclusion of the revolt, she sealed away her younger twin brother, Inorganic Angel Rosiel, within the Earth, emotionally unable to fulfill his request to be killed before he became insane and destructive. Captured and branded a fallen angel, Alexiel is punished by having her body frozen and her soul endlessly reincarnated as a human whose life is full of misery. While Rosiel is freed by his subordinate Katan, Setsuna finds his life and Sara's endangered by various attempts to awaken Alexiel's dormant soul within him. Realizing they cannot bear to be separated, Setsuna and Sara run away together and consummate their love, in hope of starting a new life together. Sara eventually dies protecting Setsuna from one of Rosiel's subordinates. Devastated, Setsuna awakens Alexiel's soul, causing widespread damage. Adam Kadamon, the angel closest to God, intervenes by turning back time to just after Alexiel's awakening and freezing time on Earth; she then tasks him with freeing her from her imprisonment. To search for Sara's soul, sent to Hell for incest, Setsuna's body enters a near-death state, and his soul searches for hers, eventually learning that it has been taken to Heaven. Sara, meanwhile, awakens in the body of Jibriel, the archangel of water held captive; revealed to be her reincarnation, Sara is eventually returned to her original body, but finds herself impregnated by the angel Sandolphon, whose soul resides in his brother's body and who hopes that she will bear him a body. After Rosiel absorbs him to gain his power, an act which speeds up his physical and mental decay, Sandolphon's remnants possess her, causing her to see Setsuna as a monster. Assisted by Lucifer, ruler of the demons who loves Alexiel, Rosiel unseals the Tower of Etenamenki, where God rests, with Alexiel's body. Intent on restoring the Earth, Setsuna follows him, with Kurai and the archangels of fire and earth; along the way, he aids an injured Katan, who hopes to save Rosiel before he loses his free will to do so. At the tower, Rosiel kills Katan, only to realize that he had killed the one he loved and tried to protect from himself; he then goes into a state of destructive despair. Awakening in her own body with Setsuna's help, Alexiel reveals to him that she had always loved him: because he had been born the opposite of his healthy sister, she bargained with God to save his life in exchange for her imprisonment, from which she later escaped with Lucifer, and an agreement to never show him any compassion. She then kills him, and absorbs him into her womb so that they will never be apart again. Before dying, Rosiel passes along his power to Setsuna. Setsuna and his group find Adam Kadamon's head, used to nourish the unborn angels, and learn that she attempted to prevent God's plan of destroying humanity by hiding him and the tower from the angels and freezing time in hopes that Alexiel's reincarnation could save them. Because God draws power through Adam Kadamon, the archangels and Kurai seal her up, while Setsuna confronts God and encounters Sara and Lucifer there. Sara overcomes her possession to cast out Sandolphon, and Setsuna defeats God with Lucifer's help. Time returns to normal on Earth, where Setsuna and Sara joyfully reunite at last.