The sea is not unlike the abyss; it is deadly, destructive. It hides secrets in its depths and threatens even those that know it well. The sea easily swallows life with no trace left behind. The sea can be quite similar to oblivion. But when the mood strikes them, both the oceans and the abyss can be tempted to create life instead.
Or, a complete AU rewrite from pre-canon through all five PJO books: Percy is born a little less human and a little more otherworldly than healthy. With powers he was never meant to have, and a third parent he never wanted, the plans that the Fates originally made for him will be torn asunder.
((Title from the song Dream Sweet in Sea Major by Miracle Musical.))