The Titan Apocalypse

After the Gigantomachy, demigods find out that Kronos had created a virus that turns people to man eating goliaths. Every single human without godly blood turn to 'Titans'. The demigods try to stop the bloodshed but dies. Every single demigod except Perseus Jackson, Thalia Grace, Nico Di Angelo was dead. When Percy finds out about this apocalypse during his training underwater, he rush to help but finds out that he is too late. He sets out to find survivors and finds Thalia about to get eaten, surrounded by the bodies of her hunters. After Percy saved her, Nico appeared as he just learned what was happening. Chaos, the primordial of creation, appears and give the trio a quest. A quest to another planet similar to earth, where Titans exist, to find a cure for Percy's planet.