Chapter 6

Convinced that Luffy must be a Devil Fruit eater rather than an ordinary opponent, Morgan abandons firearms and sends his troops charging in while the rubber boy is busy untying Zoro. Koby, having passed out during the earlier gunfire, comes to just as the soldiers close in. Luffy gets the swordsman free and returns his blades, and Zoro instantly locks every incoming sword against his own three. With the Marines frozen in terror, Zoro restates that he is throwing in with Luffy, since the navy will brand him an outlaw no matter what, attaching one demand: nothing in Luffy's plans may get between him and his goal of becoming the world's finest swordsman.

The brawl ignites in earnest. Luffy flattens the soldiers whose weapons are pinned against Zoro's swords, prompting Morgan to punish his own men by ordering them to point guns at their heads. Declaring himself the navy's worst nightmare, Luffy goads the captain into attacking, and Morgan proves remarkably durable, neither fighter able to drop the other. The deadlock breaks when Helmeppo presses a pistol to Koby's skull. Koby urges Luffy to keep fighting; Luffy instead lands a punch on Helmeppo. Morgan seizes that opening to strike, only for Zoro to cut him down.

Zoro walks free of the Marines and formally signs on as the first member of the Straw Hat Pirates, while Morgan falls to him. From here on, despite carrying no bounties, both Luffy and Zoro are treated as criminals. This is the second installment to ship without a dedicated cover page. The title also launches a recurring naming pattern in which certain chapters are labeled after the order in which crew members join, a motif that returns later with "The Fourth."