After years of aiding the Olympians. Perseus is repaid with betrayal.
They simply throw him away. Artemis placed him as guardian of the hunters. In hopes of his death.
A great unknown evil took over Zeus. Giving Percy no mercy. Zeus sent Percy down to Tartarus. Where the young hero was brutally tormented for millennium.
After another several millennium. Percy was rescued by the lord of the pit. And later on adopted as the son of Gaea and lord Tartarus. Taking up a deadly tittle as Prince of the pit.
Having lost him loyalty. Percy's become known as heartless, Stoic. A horrid monster who was only loyal to his parents. He gave no mercy to his enemies. None.
Soon not long after. Percy created Dragons, and became their king. Having them find mates in order to not suffer from heartbreak.
Soon Tartarus places him on a mission. Aid the Gods. Then destroy them. He went on to complete his mission which unknown to him. He would stumble across his own mate.
A human girl.
How will this affect his mission. And how will Annabeth take the news. Once knowing. She could and will be replaced by a Human girl.