Now, this is how the story begins:
The red hair puts the hope of the new world on Luffy and wants him to become the Pirate King.
Hawkeye was so idle that he wanted to fight against the red-haired man, so he took Zoro as his apprentice and asked him to become the hunter of the Pirate King.
Then...
Zoro: "Luffy, you once told you that my dream is to become the world's greatest swordsman."
Luffy: "It seems there is such a thing."
Zoro: "But Hawkeye won't fucking fight me until I chop off the Pirate King's head!"
Luffy: "Then I'll let Sanji be the Pirate King for me for two days."