“The Chosen One” aspect is really interesting in the pjo series.
Like we all know that Percy’s going to be the one of the prophecy, there’s absolutely no doubt about it.
Already ignoring the fact that he’s the narrator, there are literally huge cosmic, higher power signs pointing to Percy throughout the series, enforcing the idea that Percy is the hero of the great prophecy and his role to either save or destroy the world was predetermined years before he was even born.
But in the Titan’s Curse, two extremely interesting things occur: First, three other children of the Big Three become involved into the storyline. And as they are all under sixteen, that definitely throws the off the certainty of Percy being the hero of the Prophecy. Second, and more importantly, after Bianca’s death and Thalia’s newly immortal state, Percy makes the decision to be the hero of the prophecy. Percy chooses to be the Chosen One.
That in itself creates such an interesting and conflicting concept: Percy is obviously the One of the prophecy, but his decision implies that he had a choice in the matter. Perhaps, if he had never come to that resolution, that is one of the many ways he would have razed Olympus.
Or maybe, in order to be the chosen one, you have to choose yourself. It’s interesting to think what would have happened if Thalia never accepted immortality or if Bianca hadn’t died.
Also, I’m not sure how much this has been discussed but that is such a defining characteristic of Percy. (Whether or not the decision changed the outcome) Percy chose to be the hero of the prophecy. He deliberately accepted that as his role. And he did it all to spare someone else’s pain - so Nico di Angelo would not have to suffer more than he already did.