(art by zukorra)
Without his Achilles blessing, Percy would never have survived the Titan War. When his skin (excepting the small of his back) became like armor, he was invincible, therefore becoming the most feared demigod in the gods’ army.
He gave all that up to reach Camp Jupiter during The Son of Neptune. The Tiber River wiped the blessing away, leaving him with his mortal vulnerability.
I still don’t know if this has helped or hurt him, but whatever the case, I think we know he still has an Achilles heel. Annabeth, essentially, was always the ‘mortal spot’. In the Styx, he saw her, and she kept him mortal. In a sense, his loyalty to his loved ones has always been his Achilles heel, and it will play a huge part in the battle to come.
When the time comes, will he be ruled by his fatal flaw? Or will he be wise? I just finished rereading Last Olympian yesterday, and I have to admit- I don’t know if he’d be able to think rationally if any of his friends were in danger. He’s been through a lot. At this point, I think all he really cares about is keeping his loved ones out of harm’s way.