Simone's father was the Dimme Palackas, who escaped from his master and fell in love with a human woman. When Simone was a child, her mother and younger brother Tony were killed by demons in an attack staged to look like a robbery. Palackas knew it was only a matter a time before the demons found him as well, so he made a bargain with Jaden to suppress Simone’s demon powers in exchange for his soul, then he killed himself. Simone was sent to live with foster parents, who died a car accident when she was in college. After that, her only companion was Jesse, a ghost she met on the night of her mother's death.
Simone became a medical examiner and was investigating a death scene when she was attacked by Daimons. Xypher showed up and entered the fight. His enemy Satara chose that opportunity to send some of her brother Stryker's Spathi Daimons to attach deamarkonians to both Xypher and Simone. These were an Atlantean invention that bound a stronger being to a weaker one. In this case, Satara's plan was to bind the half-god, half-demon Xypher to a human being and kill her, thereby killing him as well. Satara sent gallu demons after Simone, not knowing that her half-demon heritage would give her immunity to the gallu's bite. However, the bite did unleash her demon powers, thus negating Palackas' bargain with Jaden.
Xypher made a deal with Jaden to remove the deamarkonians but he stayed with Simone after they were unbound because they were falling in love. He called a truce with Satara instead of killing her because his main priority had shifted from vengeance to Simone's protection. Satara demanded that Xypher kill himself instead and promised not to harm Simone. Before he could commit suicide, Satara stabbed him in the heart. He died, but Hades released him from Tartarus because Xypher's sacrifice on behalf of Simone proved that he had reformed.
While Xypher was in Tartarus, his half-brother Kaiaphas attacked Simone. Jaden appeared and bestowed Palackas' sword upon her, giving her the power to slay Kaiaphas. Jaden did this to uphold his end of the bargain with her dead father, which was to keep her safe from demons. Simone then made her own deal with Jaden. Not knowing that he had been freed by Hades, Simone offered her soul for Xypher's release. Jaden accepted it, let her die, then gave the soul to Xypher. When Xypher restored her soul, she became immortal.