Percy holds onto Annabeth's hand in the darkness.

"I love... love you." She says, and its not a surprise, because every single day they've been down here, or at least their measure of days, she says it at least once.

"I love you too." He replies, and Percy's teeth are chattering. It's so cold, so cold, down here. Who would've thought that Hell had already frozen over long ago?

"D'you think we've been down here a year?" Annabeth asks "or two? Or a hundred?"

Her skin is clammy beneath his palm, as she digs what's left of her fingernails into the palm of his hand.

"I don't know," he presses his forehead against hers "but happy birthday in advance."

She almost laughs. That's a victory.

"I have a feeling your birthdays closer. Happy birthday seaweed brain."

Percy doesn't let go of her hand as they shakily get to their feet and begin to move through the perilous caves of Tartarus.

Some time later, Annabeth says that she loves him again, and Percy says it back.

That is how they continue on.