At first Percy denies it.
He knew that the River of Styx would make his skin invulnerable; he just never thought about what that would mean.
He first notices it when he is holding hands with Annabeth.
He remembers the moment.
He had said something, Annabeth was laughing, and she had looked so beautiful, he squeezed her hand.
She squeezed back. He knew she did, he saw it.
But he hadn't felt anything.
After that moment, he couldn't stop thinking about it.
Was Annabeth's hand warm?
What did the grass feel like again?
Was the blanket that was wrapped around him soft?
This lasts for about a week.
Annabeth finds him in his cabin, in a corner, shaking.
After twenty minutes Annabeth finally gets Percy to tell her what's wrong.
He can't feel anything.
Not the ground, not the wind, not the water, not the grass, not the sand, not the blanket, not the fire, not the handle of his sword, not the air, not…anything. Half way though his rant, Percy starts crying. He can't feel the tears on his cheeks.
At this point, Annabeth pulls Percy into an embrace.
It doesn't help, Percy can't feel her. Is she warm? Is she holding him tightly or softly?
But Annabeth, the daughter of Athena, the genius, has an idea.
Percy goes completely still. He feels Annabeth's fingers on his Achilles spot.
He can feel her. Not just her fingers, her, her soul, her life, her-
Percy starts sobbing again, his tears crawling down his face, but he can't feel them.
But that's okay, because he can feel her.
Praise would be good, criticism would be great.