Koro

The invention of Caesar Clown, this poison gas reached the Beasts Pirates through underworld dealings after Donquixote Doflamingo trafficked it to them. Caesar branded his own creation a mass-slaughter weapon, and in practice its lethality overshot even what he had anticipated. The label Koro comes from korosu, the verb in Japanese for killing.

Koro is a quick-spreading toxin that infects and drains the vigor of anyone who breathes it, yet leaves them lucid enough to answer questions. Especially hardy targets can cling to enough strength to look unharmed, as Nekomamushi did. A treatment window lasts through the first forty-eight hours of exposure. Pushed by Chopper and Sanji, Caesar tapped his Gasu Gasu no Mi to conjure a counter-agent he dubbed Roko, which scrubbed away the gas that lingered but healed no one already poisoned; for them, the Roko remedy in liquid shape had to be injected into the blood so the toxin could be driven out of the body.

The gas was deployed on Zou after a grueling five-day, five-night siege pitted Jack against the island's defenders. His patience gone, Jack released Koro, and the Mink Tribe was left crippled and at his mercy, though he sailed off the following day. Soon the Straw Hat Pirates landed with Caesar among them, and when his authorship of the weapon surfaced, Sanji and Chopper thrashed him and compelled him to purge whatever gas still hung in the air and lend a hand in mixing the antidote that rescued the minks.