Chopperphage was created using liquid antibodies to the Ice Oni. It takes the form of a mist gas, and can be stored in weapons like cannons that can spread it through an entire room after firing. The initial cloud of gas bears a face resembling Chopper's.
Chopperphage briefly heats up the body considerably, eliminating the cold gas and ice that the Ice Oni spreads. Those infected will feel pain from the heat, but only briefly and to a manageable degree. The virus takes effect instantly and will eliminate the Ice Oni in a matter of seconds. It does not appear to have any effect on people not infected with Ice Oni.
Wano Country Arc
During the battle in the Skull Dome on Onigashima between the Ninja-Pirate-Mink-Samurai Alliance and the Beasts Pirates, Beasts Pirates All-Star Queen unleashed his virus Ice Oni into the crowd, infecting thousands of people on both sides. He decided to give the antibodies to Scratchmen Apoo and make it a game. If Apoo managed to keep the vile of antibodies for the one hour it would take for everyone to die from the Ice Oni, then he wins. However, Queen also threatened to kill Apoo if he lost the antibodies.
Roronoa Zoro soon managed to take down Apoo and give the antibodies to his crewmate Tony Tony Chopper, the Straw Hat Pirates ship's doctor. Chopper furiously worked to multiply the antibodies to cure the infected, which included allies, enemies, and even himself, before the Ice Oni killed them.
Since there were too many people infected to use the antibodies for injections, Chopper instead used the antibodies to develop a virus of his own that would eliminate the Ice Oni. He successfully completed the countervirus only an hour after the Ice Oni was released, and had Miyagi and Tristan fire it out of a cannon. The benign virus spread through the room and quickly healed the infected on both sides, eliminating the Ice Oni completely.
- "Phage" comes from the word bacteriophage, a fast-replicating virus that was once used as a method of fighting bacterial illnesses.