The Organic Angel Alexiel is the older of the two twin angels. She was loved by the angel Uriel and the demon Lucifer, though she claims the one she loves most is God. In truth, the one she loved most was actually her twin brother, Rosiel; though not in the incestuous way that Sara and Setsuna love each other. She was one of the two highest angels in Heaven and has 3 wings.
Born from Adam Kadmon to love God, Alexiel rebels against him because of the love she has for Rosiel. She is forced to conceal her feelings under the threat that Rosiel would be killed the moment God heard any declarations of love from Alexiel to her brother. She is also sentenced to be confined in Briah, the Angel's Garden (Eden), and forced to eat the fruit of the Tree of Life. This act is damning her, because the tree is grown from part of Adam Kadmon's body - she is technically eating another angel's flesh.
It is also in Eden where Alexiel and Lucifer first meet. After God had revealed his plan to Lucifer, that Lucifer would start a war against heaven and become evil, Lucifer wanted to take revenge by corrupting and killing God's "beloved" daughter. After speaking with her, he changes his mind and promises to break her out of Eden, which he later does. This, however leads to the erasing of his memories and imprisonment of his soul into Nanatsusaya, which Alexiel later finds and fights with.
When she seals Rosiel away, she is imprisoned and tried by the High Council for her actions. After lying that the one she loved most was God, Uriel sentences her body to be imprisoned in the angel crystal while her soul is endlessly reincarnated into a human without end; each of her lives are to be miserable and end in a painful death.