Lilith

Lilith is the sister of the seven brothers. She was gravely injured during the Great Celestial War due to attacks from the opposing angels and fell down from the Celestial Realm. Beelzebub claims to be disturbed and saddened by the fact that he was unable to save both of his siblings during the war and was only able to shelter Belphegor during the time of the attack.

Upon finding her dying, Lucifer swore his loyalty to Lord Diavolo in order to have her saved. Diavolo had her reincarnate as a human. She lived a happy life, having lost all of her memories from her life as an angel. When she died, she regained the memories of her brothers and her life in the Celestial Realm. It is revealed that the main character is a distant descendant of human Lilith.