" What was I thinking?" Chiron cried. " I can't let you get away without this."
He pulled a pen from his coat pocket. It was an ordinary disposable ballpoint, black ink, removable cap. Probably thirty cents.
Gee," I said. "Thanks."
Percy, that's a gift from your father. I've kept it for years, not knowing you were who I was waiting for. But the profecy is clear to me now. You are the one.
I remembered the feild trip to the Metropolitan Museum of Art, when I'd vaporized Mrs. Dodds. Chiron had thrown me a pen that turned into a sword. Could this be...?
I took off the cap, and the pen grew longer and heavier in my hand. In half a second, I held a shimmering bronze sword with a double-edged blade, a leather=wrapped grip, and a flat hilt riveted with gold studs. It was the first weapon that actually felt balanced in my hands.
The sword has a long and tragic history that we need not go into," Chiron told me. "It's name is Anaklusmos."
Riptide," I translated, surprised the Ancient Greek came so easily.
Use it only for emergencies" Chiron said, "and only against monsters No hero should harm mortals unless absolutely, of course, but this sword wouldn't harm them in any case. "

― Rick Riordan