It's the 20 anaversery of Percy and Annabeth's underwater kiss. Percy was now 320. Annabeth had been driven insane by the memory's of their trip to Tartarus, the people they lost in the war with Gaia, the war with Kronos, losing Luke. Thalia had died on the hunt, and that had hurt Annabeth so so much that not even Percy or Dionysus could bring her back to sanity.
Eventually it got so bad that they had to kill her. Nobody wanted to. They all loved her and Percy fought as hard as he could but they held him back as they sedated Annabeth and cut her throat to put her to rest.
The Gods were cruel and made Percy immortal. He would always live with this pain. Eventualy all of his friends died. Even Ciron died. He was stabed in the back by a cyclops when he had his back turned. Percy eventually went insane from the loneliness and confronted the gods.
