Y.T. is a great character. Her name, or her initials if you prefer, stand for Yours Truly. She is one of the main female protagonists of the story, and the reader is told that she is fifteen years old. When the reader meets Y.T. for the first time, she is working as a kourier (spelling intentional). She's a messenger on a skateboard with an electromagnetic "poon" (harpoon) that she can sling and attach to cars.
From the moment the reader meets Y.T., it's obvious that she is a brave girl. Her job alone is a dangerous profession. Drivers do not take kindly to being pooned, and they make it their mission to wreck her on the side of the road with very fast, evasive driving. None of those techniques work, because Y.T. is a streetwise kourier. She knows what to expect from the drivers and she knows how to avoid their attempts to harm her. I also think that Y.T. has a good sense of humor. Each time that Hiro attempts to get Y.T. off of his car, she slaps a sarcastic and insulting sticker on his window . . . while skating at 60 mph behind his car.
The Kourier leans back -- the Deliverator can't help watching in the rearview -- leans back like a water skier, pushes off against his board, and swings around beside him, now traveling abreast with him up Heritage Boulevard and slap another sticker goes up, this one on the windshield! It says SMOOTH MOVE, EX-LAX
Lastly, Y.T., despite her snarky, street-wise antics, is not heartless. She could have left Hiro and his pizza on the side of the road. She could have let the pizza expire, and Hiro would have been killed by the mafia for it. Delivering the pizza on time is not her problem, but instead of moving on and harpooning another car to get out of the neighborhood, she takes the pizza from Hiro and makes it her mission to get it delivered on time.
"Where?" she says. "Where's the pizza going?"
He's going to die and she's gamboling.
"White Columns. 5 Oglethorpe Circle," he says.
"I can do that. Open the hatch."
His heart expands to twice its normal size. Tears come to his eyes. He may live.