Lady Death originated as the sexy and violent villain that was perceived as a hallucination by the boy Ernest Fairchild. She promised to "love Ernie forever", love he never had, in exchange for his loyalty. That loyalty was to kill everyone on Earth. In the beginning, she had no real purpose or personal story except to be the Eye-candy for Evil Ernie's comic book, and she was just seen as the evil sadistic woman who would always give Ernie the incentive to kill. As the story progressed, Lady Death detached herself as the girlfriend of Evil Ernie, and began her own story. With the change, her personality changed dramatically from the sexual villain to a full blown hero.
The setting for the original Lady Death comic was medieval Sweden. The woman who would become Lady Death was born a mortal named Hope. Her father was a local nobleman named Matthias who was forcibly conscripting peasants into military service as feudal levies. The exact nature of the war that Matthias was prosecuting is not specified, although evidence from the recent revision of the character by Avatar Press suggests that it may have been one of the Northern Crusades (also known as the Baltic Crusades).
Unknown to his innocent daughter, Matthias had a dark secret. Although congratulated by the Church for his work against the pagans, he was despised by the common folk as a cruel tyrant. Matthias was outwardly pious, but secretly dabbled in black magic and demonology. He was actually a descendant of the fallen angels who had led the rebellion against God. By contrast, Hope's mother was a woman so pure and innocent that her bloodline reached Heaven. Hope's mother died when Hope was still in her late teens, and she was left to live with her father.
Eventually, Matthias' cruelty triggered a peasant uprising. Matthias narrowly escaped death at the hands of the rebels by summoning a demon, but Hope was captured by the rebels and accused of witchcraft. Faced with the prospect of execution by burning at the stake, Hope uttered an incantation that she had overheard her father use. This incantation summoned a demon who offered her a bargain -- he would rescue her from death if she would renounce her humanity and serve the powers of Hell. Hope accepted the bargain and was transported into the infernal realms.
Once in Hell, Hope became entangled in a civil war that was raging between Lucifer and an army of renegade devils led by a powerful sorcerer. Hope was devastated when she learned that the ambitious sorcerer challenging Lucifer for the control of Hell was her own father.
Gradually corrupted by the nature of her surrounding, Hope was tainted with evil. She allied herself with an exiled craftsman who forged weapons for the infernal armies. While speaking to him, she declared that the innocent woman she had once been was dead and that she would henceforth only be known as Lady Death.
In her new persona, Lady Death led an uprising against the Lords of Hell. During the final battle, Lucifer cursed her never to return to Earth while the living walked. Lady Death swore an oath that she would circumvent Lucifer's curse by exterminating all life on Earth.
Lady Death finally ended Lucifer's control over her by casting him through Heaven's Gate (a place where evil cannot go), and in doing so became the new ruler of Hell. Many of the beings living in hell believe that the ascension of Lady Death signaled the beginning of the age of judgment - the final battle between good and evil for the fate of the Earth.
Story of Joining Sora's Team
When Sora was seperated from the team in the Gummi Ship, after an aerial battle, Lady Death nursed him back to health when he landed in her world. Soon when Sora woke up, Lady Death's servants brought him some refreshments, and as Sora was greatful, Lady Death brought Sora's Keyblade all polished and clean. When after Lady Death explained about Sora landing from the sky, Sora thanked her and granted her a Dream Eater (Spirits) for a pet. Before Sora left, Lady Death asked about where was he from, and doing in her realm. After Sora explained everything, she volunteered her assistance to help reunite with his friends. When Nobodies, and Castlevenoms appeared, the two formed a combonation attack which defeated them with one hit. After their victory, the Keyhole appeared and as Sora opened the new pathway, Lady Death asked to join Sora's team to help on his journey.