|This article is about a/an event in Kamen Rider Ex-Aid.|
Little is known about the details of Zero Day. The outbreak was claimed to have been caused by a glitch in the 10 games that Genm Corp. was developing at the time, from which the Bugsters' data came from. However, it is is later revealed to have been intentionally started by Kuroto Dan, who framed his father, Masamune Dan, to cover his tracks. Despite their use to combat the outbreak, it is implied that the Proto Gashats were the source of the virus.
The event was never made public, but many people were infected and died from the outbreak, including Hiiro Kagami's girlfriend Saki Momose, who was the host of Graphite; Genta Uesugi, the son of police detective Heiji Uesugi; and Kiriya Kujo's friend Jungo Aihara, who committed suicide before the infection was able to kill him. Taiga Hanaya became Kamen Rider Snipe in order to combat the infection and stop Graphite. However, he failed to defeat him, resulting in Saki's death and Taiga being stripped of his medical license and Gamer Driver.
5 years later, Graphite used the Proto Drago Knight Hunter Z to spread an infections of a comparable scale to Zero Day, but was killed by the four Hunter Gamer forms of doctor Kamen Riders Ex-Aid, Brave, Snipe, and Lazer.
While interrogating Masamune about Zero Day, Detective Heiji Uesugi contracted the Bugster virus, leading Emu Hojo and Asuna Karino to Masamune, who revealed to them that Kuroto caused Zero Day after discovering the Bugster Virus in the wake of the Y2K incident.
It is later revealed by Kuroto that the data of all people erased by the Bugster virus, including the victims of Zero Day, is stored in the Proto Gashats.
List of victims
After the defeat of Masamune, Emu holds a press conference where he lists all victims of the Bugster virus and vows to find a way to revive them from their data.
The victims of Zero Day and related incidents are:
- Haruo Takaoka
- Genta Uesugi (victim of Zero Day)
- Jiro Maki (contracted Game Disease from the Proto Bang Bang Shooting Gashat before Zero Day)
- Saki Momose (host of Graphite during Zero Day)
- Kiriya Kujo (killed by Kuroto for investigating him, his revival was not made public)
- Sakurako Dan (host of Poppy Pipopapo before Zero Day)
- Masamune Dan (former suspect, committed suicide to avoid punishment for the Kamen Rider Chronicle incident)
- Kuroto Dan (killed by Parado, his revival was not made public)
- Zero Day's name is derived from "zero-day vulnerability", a term used in computing to refer to an undisclosed computer software vulnerability exploited by hackers, affecting computer programs, networks, and so on. It is usually not publicly known before becoming active, resulting in little to no time to resolve the issue and mitigate its actions, thus the term "zero-day". The fact that the Zero Day event was never made public, and that it was caused out of a sudden by a glitch in the games developed by Genm Corp. which led to the spawning of the Bugsters, further alludes to the "zero-day" term used in computing.
- The name also connects to the usage of the medical term "Patient Zero", a label for the first person infected in a disease outbreak.
- Despite this event claiming to be where the Bugsters first appeared, this is technically an incorrect statement as Asuna Karino is a Bugster herself and appeared sometime prior to the events of Zero Day.
- The virus itself seems to also have existed sometime before Zero Day's occurrence, as Emu Hojo was already implanted with the virus during a surgery one year before Zero Day.
- Episode 21 shows that the virus was created in 2000, partly due to the Y2K bug, and its true nature was hidden by Kuroto to avoid suspicion.