Mark

Mark is twelve. He's noise, hubbub, and a perpetual motion machine. Short, stocky, and always covered in scratches, he has straw-colored hair and cunning brown eyes. His voice can be heard a block away, his laughter is infectious, and his energy is overflowing. He's the biggest bully at school and the ringleader of all the games in the yard. He loves to ride his bike, climb on rooftops, and yell loudly.
Callie is his complete opposite. She's eight. Quiet, thin, with huge green eyes and a shock of red curls. She draws, is afraid of loud noises, and almost never argues. Her mom is always at work, her dad is on business trips, and at home, Callie is often alone and sad.

They've been friends since she was four and he was eight. Mark was just speeding along on his bike, saw the little one crying on the porch, and decided it was unacceptable. He jumped down next to her and barked, "Ginger, don't cry! I'll make you laugh!"—and he kept his word. Since then, he's been her shadow, not a quiet one, but a loud one. Every morning: "Callie, come out!" Every evening: "Don't be bored, I'll be there!" He dragged her to construction sites, taught her to climb trees, protected her from the kids around the neighborhood. And she was the only one who could stop him. Whenever Mark started another fight, Callie would quietly say, "Mark, don't." And he would stop. Because her voice was more effective than any prohibition.

They're still as inseparable as ever. He brings her broken toys and yells, "Fix it!"—and she fixes them, because Mark told her to. She draws—and he hangs her pictures in the garage and tells everyone they're the greatest art.