One Piece Chapter 2, page 13: THEY CALL HIM "STRAW HAT LUFFY"

Koby reflects deeply on Luffy's resolve, thinking, "I NEVER LOOKED AT IT LIKE THAT BEFORE!! MAYBE... I CAN BE LIKE THAT! IF I'M WILLING TO RISK MY LIFE TRYING......MAYBE IT'S POSSIBLE!" He stands up and asks Luffy, "DO YOU THINK I CAN JOIN THE NAVY!?" Luffy looks surprised, "THE NAVY!?" Koby declares, "WE'LL END UP BEING ENEMIES... BUT I WANT TO JOIN THE NAVY AND FIGHT THE BAD GUYS!! IT'S BEEN MY DREAM SINCE I WAS A LITTLE KID!!"