One Piece Chapter 5, page 13: CHAPTER 5: THE KING OF THE PIRATES AND THE MASTER SWORDSMAN

Zoro continues to lecture Kuina, shouting, "SOMEDAY I'LL BEAT YOU BECAUSE I WORKED HARD, NOT BECAUSE YOU GOT WEAKER!! IT'S GOT NOTHING TO DO WITH BEING A BOY OR A GIRL!! I'M TRAINING ALL THE TIME TO BEAT YOU! YOU'RE MAKING ME LOOK BAD!" Kuina listens quietly. Zoro then proposes, "LET'S MAKE A PROMISE TO EACH OTHER! SOMEDAY, ONE OF US WILL BECOME THE GREATEST SWORDSMAN EVER!! WE'LL FIGHT EACH OTHER FOR THE TITLE!" Kuina, crying tears of joy, smiles and calls him a "YOU IDIOT! YOU'RE TOO PUNY!" Zoro firmly declares, "IT'S A PROMISE!" as they seal their pact.