Once Upon a Time (He Delivered Hell in a Handbasket)
Hades was the god of death. Therefore, they couldn't lock him up without magick. There'd be no death. Everyone would be immortal. And the Olympians were selfish. They kept immortality for themselves. So instead of leaving Hades on the Isle of the Lost, they put him on house arrest, and whenever he had a demigod child, the gods would have them delivered straight to the Isle.
So when he and Persephone had a beautiful, bouncing baby daughter, the gods were lost. She was, essentially, one of them. But she had the potential (according to Apollo) to ruin them.
So when they voted, and the majority wanted to keep her on the Isle, that's where she went. Forever. And so what if she had no parents? So what if she was left in a blanket on the Isle with no one to raise her? So what if that blanket was stolen not even an hour later? One little girl's death wasn't even a pinprick on the gods' conscience. If they could kill their own mothers and fathers, why couldn't they kill their own children? Or, better yet, why couldn't their children kill them? It was a miracle she survived.
Her name was Hayley, she was the daughter of Hades, and she'd reign terror on the Olympians one day. They just didn't know how soon.
Even though she'd never even met her father, she was the sole heir of the Underworld. Beautiful. She'd make them pay for making her live on the Isle when she could've been a princess. in the meantime, she settled for being princess of the criminals, the thieves, the liars and murderers and rapists, because she wasn't a queen, would never be as long as she remained on the Isle of the Lost, under the Daughter of Maleficent and the Daughter of Grimhilde, the queens of the Isle, the queens who were more than willing to put their subjects to death, the subjects that were too evil for them {but because a goddess has no conscience, Hayley ruled them with pride}.
Hayley learned to create potions and poisons and manipulations. She could create a better sleeping potion than Queen Grimhilde {but, not her daughter}, had killed more people than Maleficent (everyone had, but no one knew {other than Mal le Fay}) and was richer than Angelique Mors (everyone came to death eventually, may as well know who they truly were now). Hayley was almost perfect, and she prepared for the coming of the prophecy. She waited and waited and then she was eighteen and the Queen's moment came and nothing
Hayley built an army for when she finally took over. An army of the dead. She killed all the most ruthless unknowns of the Isle's underground so that she could lead the dead to a new era of victory (for her, all for her, they were dead). All she needed was a way off this pathetic island with its pathetic inmates. Then High Queen Mal killed her husband.
When she was released, the first thing she did was simple. She tossed dearest daddy and mummy who couldn't have given a damn about her when she was on the Isle into Tartarus. Then she took the throne. So what if she lost her soul? Souls were practically worthless in the Underworld. They were everywhere. Technically, she died when she took the throne. But she gained so much more, including a son {and a lover} and a family in the Kings and Queens.
And when she lead her armies of the dead, the ruthless and the cunning and the damned onto Olympus, and she threw Zeus down to the mortal world like he'd done to her so many years ago, and when she carved out Aphrodite's pretty face and took a knife to the wheels of Apollo's chariot of the sun, she smiled. Her job was done. She'd killed them all. She would lead the true gods and goddesses into a new era, an era of pain and terror and bloodshed. And when she sat on her throne of bones in her dress of souls and drank blood from her cup, she was finally satisfied.
(Because maybe she couldn't kill the gods, but she could sure as hell make them suffer.)
When a Goddess comes of age,
Four shall break her magick cage.
They release a demon into the wild.
Changing the fate of the hero's child.
A final Queen of Olympus and Hell.
Gods and Goddesses to sound the death knell.