Sacrifice

Guilt has begun to eat at the demigod son of Poseidon.

After two wars, the deaths of his friends and loved ones have begun to haunt Percy.

In his cries of anguish and guilt, the demigod whispers an oath that can never be broken, lest his souls be claimed by the river Styx.

"Give me the chance to redo everything, and I will save them all, even if it costs me my life. I swear it on the Styx."

And with those last words, the son of the sea disappeared in a cloud of ocean mist.