Shinokuni is a chemical weapon created by mixing compressed H2S gas with a candy containing an unknown substance.
The poison gas spreads at an incredible speed, and petrifies any organic victims that are caught within it as it enters their skin and body, trapping the victims in a shell where the substance sticks to surfaces like ash. However, if the petrification shell is broken open within half a day of the initial infection, then the victims can still be saved.
When Caesar Clown decided to debut his newest gas weapon to brokers across the world, he lured Smiley with a piece of "bait" in the shape of a giant candy, which, when devoured, had Smiley regress back into his original gas form, with the bait's ingredients converting the H2S gas compound into an even deadlier form, decimating many of Caesar's centaur subordinates.
When Caesar was being cornered by Luffy to no end, he decided to let the Shinokuni gas flow into the lab and absorb the petrifying smoke into his body, which greatly enlarged him. He then claimed that two peaceful countries already wanted to purchase Shinokuni due to seeing the potential, and poured the gas onto his underlings as an exhibition for his criminal underworld spectators.
- One Piece Manga and Anime — Vol. 68 Chapter 676 (p. 9-10) and Episode 602, Smiley is reborn as Shinokuni.
- One Piece Manga and Anime — Vol. 70 Chapter 696 and Episode 622, Caesar tortured into revealing the cure.
- One Piece Manga and Anime — Vol. 70 Chapter 691 (p. 12-13) and Episode 617, Caesar merges with the Shinokuni.