The Demon Lord of Hell, his angelic name is Lucifel/Lucifael, varying according to translation. He is also the twin brother to the angel Michael. Just when he was exalted to the position of Morning Star, he was told by God that he was born with only one reason - to become the Prince of Darkness and rule the evils and demons. Angry with this revelation, he decided to go rape Alexiel in order to enrage God since in Heaven, it was believed that Alexiel was actually God's "beloved daughter". The reality was that YHWH/God actually only used her and wanted her out of the way so he could follow though his plan; Lucifer had no way of knowing this. However, he fell in love with her when he found out she was not the cold emotionless woman everyone believed her to be, but a woman who loved everything with a love that encompassed anything Lucifer had seen. He fell in love with the "woman with the same eyes as him". He leaves Eden after kissing her and continues to stage a rebellion against God.
When he and his comrades fell, they found that hell was a barren land incapable of supporting life of any kind, so he rooted his body to Hell's ground, merging with it in order to make Hell habitable. Thus when Hell's earth breaks, it is his blood that gushes out. He later returns to Eden a second time to free Alexiel from her God-made prison, and thus assisted in bringing forth the second rebellion, which Alexiel staged.
As his punishment for assisting Alexiel's escape from Eden, God extracts his soul and imprisons it in a seven-bladed sword, Nanatsusaya Mitamanatsurugi. His soul was imprisoned in the sword for so long, he forgot all his memories. A number of people tried to wield the sword and failed until Alexiel came along. He allowed her to control him, because she was the woman that held all his memories in her hand. As Nanatsusaya, Lucifer hated Alexiel because he was helpless as she knew more about him than he did and she would never reveal his past to him. But when Alexiel was captured by the angels and sealed in the Angel Crystal, Nanatsusaya followed her through all her reincarnations. He deludes himself into thinking that it is because he hates her and wants to see her suffer, but in the end his actions prove otherwise.
He later helps Setsuna defeat YHWH