One Piece Chapter 2, page 12-13: THEY CALL HIM "STRAW HAT LUFFY"

Koby continues to panic, shouting, "DO YOU WANT TO DIE!? EVERY PIRATE IN THE WORLD IS AFTER THAT!!" Luffy calmly replies, "AND SO AM I." Koby screams, "BUT THE ODDS AGAINST YOU ARE ASTRONOMICAL!!? YOU WANT TO BE THE KING OF THE PIRATES IN THE GOLDEN AGE OF PIRACY!? IT'LL NEVER HAPPEN!! IT'S IMPOSSIBLE!!" Suddenly, Luffy punches Koby on the head with a loud "KLONK". Koby rubs his head, crying, "HEY! W-WHY'D YOU HIT ME!?" Luffy simply says, "YOU WERE HYSTERICAL." Koby grumbles, "OKAY, I'M USED TO IT." Luffy smiles and says, "I'M NOT AFRAID TO DIE, KOBY! I'VE SET MYSELF TO BECOME THE KING OF THE PIRATES... AND IF I DIE TRYING... THEN AT LEAST I TRIED!" Koby is deeply struck by Luffy's words, thinking, "WHAT GUTS... WHAT DETERMINATION!! Y-YOU'RE NOT EVEN AFRAID TO DIE!?

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!!