The virus is fused with a chilling gas, and once this gas is spread through the body the virus is able to reproduce in it, causing the victim to feel extremely cold as ice covers their skin. The ice will take on a demonic shape, causing a pair of horns and sharp fangs to manifest on the victim's head and mouth, giving them the appearance of an oni.
Once their body is covered in ice, the victim appears to lose their sense of reasoning and enters a berserk state, targeting anyone around them, ally or not. Moreover, they receive a boost in physical strength and durability due to an increase in muscle mass, meaning they are nearly impossible to defeat through conventional means (Zoro compared their endurance to that of Zombies, as they are able to immediately get up after being struck down). According to Chopper, the virus' symptoms cause too much strain on the victim's body, leading to their eventual death in around a hour at best, as confirmed by Queen.
This virus can quickly spread from person to person through physical contact, with one victim being shown biting an uninfected person to transmit it. Because of this, fighting back the infected requires one to use a weapon or another object to avoid physical exposure to the virus. The only way to cure Ice Oni is through an antibody created by the virus's developer himself, Queen, who happens to have the only known existing sample. However, it only infects living people. Brook came into contact with the virus, but did not suffer its effects since he is already dead and does not have any skin or blood.
Additionally, the progress of the virus through the body can be halted if the victim stands next to a source of fire, as the heat will eliminate the cold gas and prevent the virus from reproducing. Marco's devil fruit ability can reverse the transformation by increasing the victim's body heat to a point that the frost disappears, but this is only a temporary solution as the virus still lingers within the victim, resuming the infection process once their stamina runs out.
Four Emperors Saga
Wano Country Arc
When war broke out at the Live Floor in Onigashima between the Ninja-Pirate-Mink-Samurai Alliance and the Beasts Pirates, Queen fired Excite Bullets from a gatling gun at the enemy samurai, intending on closing off the room and spreading the virus to everyone in it.
- This virus is named after the children's game "freeze tag", which is known in Japan as "Ice Oni" (こおり鬼 Kōrioni?).
- The effects of Ice Oni resembles the traditional depictions of a zombie apocalypse in fictional media, which sometimes have highly infectious viruses act as the catalyst for it.
- When Hyogoro was infected with the virus, the physical enhancement symptom caused him to bulk up, restoring the strength that he wielded before Kaido took over Wano.
- One Piece Manga — Vol. 98 Chapter 993 (p. 5-6), Ice Oni is first seen.
- One Piece Manga — Chapter 997, Chopper explains how the virus works.
- One Piece Manga — Vol. 98 Chapter 994 (p. 10-13).
- One Piece Manga — Chapter 995 (p. 12).
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