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Koro is a chemical gas weapon invented by Caesar Clown[2] and used by the Beasts Pirates who acquired it after Doflamingo trafficked it.[3] It is described as a mass slaughter weapon.[4]


Koro is a poisonous gas that spreads quickly, infecting and weakening those that breathe it in, though leaving them conscious enough to be interrogated.[5] Its effectiveness surpasses the expectations of its own creator, Caesar Clown.[6]

However, extremely strong and resistant victims of the gas can retain some of their strength, to the point of convincing others that they had not been poisoned at all.[7] Additionally, its effects are treatable during the initial 48 hours after exposure,[8] and with the help of Caesar himself, Tony Tony Chopper managed to develop an antidote for the poison.[9]


Mink Tribe Given The Koro Antidote

An antidote is given to those poisoned by Koro.

Under pressure from Tony Tony Chopper and Sanji, Caesar created a gas to completely neutralize Koro's effects and named it "Roko". Roko managed to eradicate Koro's residue,[10] but did not cure those who were poisoned by it; instead, the poison had to be expelled from their bodies by injecting a liquid form of the antidote into their bloodstreams.[9]



After five days and five nights of battle between the Beasts Pirates and the Mink Tribe, Jack lost his patience and unleashed Koro to poison the minks, who were left incapacitated and at his mercy.[3]

However, Jack left one day after releasing the weapon, after which the Straw Hat Pirates arrived, bringing along the weapon's inventor, Caesar Clown. Revealing he was the inventor of such a weapon, Sanji and Chopper beat him up before forcing him to neutralize the remaining gas and help produce an antidote, saving the minks.[11]


  • "Koro" is derived from the word "Korosu", which means "to kill".


  1. One Piece Manga and Anime — Vol. 79 Chapter 795 (p. 4) and Episode 739, The Straw Hats encounter Koro upon arriving at Zou.
  2. One Piece Manga and Anime — Vol. 81 Chapter 808 (p. 17) and Episode 760, Chopper reveals that Caesar's gas weapon defeated the minks.
  3. 3.0 3.1 One Piece Manga and Anime — Vol. 81 Chapter 810 (p. 7-8) and Episode 760, Jack unleashes Koro against the minks.
  4. One Piece Manga and Anime — Vol. 81 Chapter 811 (p. 3) and Episode 761, Caesar describes Koro as being a "mass slaughter weapon".
  5. One Piece Manga and Anime — Vol. 81 Chapter 810 (p. 8-10) and Episode 760, The minks are interrogated while suffering from the effects of Koro poisoning.
  6. One Piece Manga and Anime — Vol. 81 Chapter 811 (p. 3) and Episode 761, Caesar admits that Koro's effectiveness has surpassed his own expectations.
  7. One Piece Manga and Anime — Vol. 81 Chapter 816 (p. 10) and Episode 767, A member of the Beasts Pirates is shocked by Nekomamushi's resistance to the Koro gas.
  8. One Piece Manga and Anime — Vol. 81 Chapter 811 (p. 12) and Episode 761, Chopper reveals that Koro can be treated within the first 48 hours after exposure.
  9. 9.0 9.1 One Piece Manga and Anime — Vol. 81 Chapter 811 (p. 13-14) and Episode 761, Chopper creates and uses a liquid antidote for Koro's poison with Caesar's help.
  10. One Piece Manga and Anime — Vol. 81 Chapter 811 (p. 6-7) and Episode 761, Caesar neutralizes the Koro gas with Roko.
  11. One Piece Manga and Anime — Vol. 81 Chapter 811 (p. 3-7,13-14) and Episode 761, Upon learning of Caesar's creation of the Koro gas, Sanji and Chopper coerce him into neutralizing it and treating its victims.

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Beasts Pirates
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Fighting Style Based: Haki
Other: Koro
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Story Arcs: Jaya Arc  •  Sabaody Archipelago Arc  •  Marineford Arc  •  Punk Hazard Arc  •  Dressrosa Arc
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Fighting Style Based: Haki  •  Rokushiki  •  Cloning
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Story Arcs: Reverse Mountain Arc  •  Whiskey Peak Arc  •  Little Garden Arc  •  Alabasta Arc  •  Water 7 Arc  •  Sabaody Archipelago Arc  •  Fishman Island Arc  •  Punk Hazard Arc  •  Dressrosa Arc  •  Zou Arc  •  Whole Cake Island Arc
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