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This article is about a/an monster race in Kamen Rider Ex-Aid.
Kamen Rider Ex-Aid
Bugster (Bacteria)
Led by: Parad
Generals and other Notable Members: Graphite
Kuroto Dan (deceased)
Ren Amagasaki
Monster Types: Bugsters
Grunts/Footsoldiers: Bugster Virus
Battled: Kamen Rider Ex-Aid
Kamen Rider Brave
Kamen Rider Snipe
Kamen Rider Lazer
Coexisted with: Genm Corp.
Next Genome Institute
Other factions battled: Shocker
Chronological/Production Order

The Bugsters (バグスター Bagusutā), otherwise described as game illness (ゲーム病 Gēmu-byō), are a type of computer virus and the main antagonists of Kamen Rider Ex-Aid.


The Bugster virus is a variety of computer virus, born from glitches caused by Y2K. The original Bugster virus was secretly injected into Emu Hojo, and extracted 10 years later to create the basis for all modern strains. Unlike most malware, the Bugster infects human beings, replicating until they take over their host's bodies, eventually causing the host to disappear and be completely taken over. The only way to treat the victim is to use the Gamer Driver to remove the Bugster from the host and then destroy it before the virus completely takes over.

Many patients appear to be singled out and infected directly with the Gashacon Bugvisor. The growth of the virus within the patient is triggered by stress, leading to a weakening of the patient's immune system. When it first flares up, the infection takes over its host's body, transforming it into a giant virus-like Bugster Union monster. Bugster Unions which host patients can only be defeated by a Kamen Rider in Level 1; the reason why is unexplained, though it may be because other Levels are too strong and may injure the patient inside the Union. Once the Union is defeated, the Bugster itself manifests from the virus debris, and can call Bugster Virus foot soldiers to help them fight. The patient begins fading away, eventually will fade completely and die, letting the Bugster become a complete being.

There are two ways to cure the patient from Game Disease:

  1. Defeat the Bugster who infected the patient.
  2. Perform a "GAME CLEAR" according to the rules of the game that the Bugster infected, so the Bugster may survive depending on the rules.

The only currently known complete Bugsters are Graphite and Poppy Pipopapo. If a patient dies from some other means first, it appears as if the Bugster connected to them will also eventually die.

The appearance and personalities for Most Bugsters are initialized from characters from the video games that they have infected. However, some Bugsters can later develop their own individual personalities by breaking their character motifs.

As hinted by Parad, unlike humans/riders who will be "Game Over" if killed, Bugsters can always "Continue" to infect more victims. It was demonstrated by the reappearance of Salty Bugster. It was later revealed that Bugsters who have achieved their complete forms can be brought back at any time whenever they are destroyed.

If a Bugster is killed or before gaining a stable body, they can be absorbed and preserved into a Gashacon Bugvisor in a form of data, as an efficient way to ensure the survival and the existence of Bugsters. They also can be released in any time.

Bugsters can also "Level Up" like game characters, in a similar manner of the mutation of general viruses to survive vaccines.



Bugster Virus Y2K

Bugster virus on Kuroto's computer screen in 2000.

Though long kept a secret, the Bugster virus was born from a computer glitch in the year 2000 caused by the Y2K event, appearing on the laptop screen of then-teenage programmer Kuroto Dan. Chasing the Mystery!

Kuroto would later install this original version of the virus into a game known as Mighty Action C, and sent it to a fan of his known as Emu Hojo, causing Emu to become the first person to be infected with the Bugster virus. The virus would continue to mature in Emu's body until 2010; having watched over Emu, Kuroto hired Michihiko Zaizen of the Next Genome Institute to operate on Emu and harvest the virus. The harvested virus was then modified and infected into Genm Corp.'s game lineup to create at least ten unique strains.Engineered History!

Zero Day

The first Bugster outbreak took place in 2011 through an event designated "Zero Day". CR was founded by the joint efforts of the Ministry of Health and Seito University Hospital to fight the Bugsters. Kuroto helped design the Gamer Driver and Proto Rider Gashats as a method of counteracting the virus. Unknown to anyone else, Kuroto was merely using the Riders and the Bugsters as an opportunity to gather data for better games.

While the outbreak was mostly contained, there were at least three casualties, including Heiji Uesugi's son and Saki Momose (coroner Jungo Aihara was also infected, but he died in a car accident before the virus could manifest). The Rider for CR, Taiga Hanaya, lost his medical license for failing to save Momose. Genm Corp. CEO, Kuroto's father Masamune Dan, was framed for the outbreak and arrested for bio-terrorism.

Second Outbreak

In 2016, the Bugster virus re-emerged. The first known victim was a boy named Sota Suyama, who was infected by the Salty Bugster. Hoping to make the boy feel better (and not realizing the severity of the condition), his doctor Emu Hojo brought him to the release of Mighty Action X, where the Bugster took over Sota's body. In the resulting chaos, Emu was able to use the Gamer Driver and become Kamen Rider Ex-Aid, removing the Salty Bugster and defeating it, saving Sota. I'm a Kamen Rider!

Soon, more Bugsters began to appear as they were fought and defeated by the Kamen Riders. Graphite tried to start off a second Zero Day by using the Proto Drago Knight Hunter Z Gashat to spread the Bugster virus over a widespread area, but he was later defeated by the Kamen Riders. In an effort to find out the truth behind Zero Day, medical examiner Kiriya Kujo went to Masamune Dan, but Kiriya was later killed at the hands of Masamune's son Kuroto.

As part of his masterplan to complete Kamen Rider Chronicle, Kuroto began to create leveled-up Bugsters such that he could collect their data once they were defeated. But after Kuroto was killed, Parad took over his project in his own way.

Chou Super Hero Taisen

As Kamen Rider Para-DX, Parad joined in the Chou Shocker Taisen, fighting in a temporary alliance with his Rider adversaries as well as Sentai RangersIcon-crosswiki against the army of Shocker from the Game World. Kamen Rider × Super Sentai: Chou Super Hero Taisen

The Perpetual Horde

As a result of Kuroto Dan's plot to revive in the Game World, an endlessly reviving horde of Bugsters emerged in the real world where they were held off by Kamen Riders Brave and Snipe while Emu was sent from CR to the Game World to stop Dan. Maze 2: Escape Ultimately, the Bugster army was suddenly dissipated in an instant as the destruction of the Game World brought about by Kazuma Kenzaki thwarted Dan's ambition to revive. Maze 3: Gorider Forever

Kamen Rider Chronicle

Other Events

"Tricks": Virtual Operations

Bugster Virus appeared in virtual simulation where Ex-Aid and Snipe was testing their powers. Ex-Aid Chapter Snipe Chapter

Kuroto Dan simulated his own Proto Mighty Action X Gashat and faced Graphite who sneaked into VR world. When asked why, Graphite simply said that he needed to test his competence, too. Dan then transforms and activates his Critical Strike finisher using the Kimewaza Slot Holder and cleared the simulation by beating Graphite.Genm Chapter

Dr. Pac-Man vs. Ex-Aid & Ghost with Legend Rider

Kamen Rider Heisei Generations: Dr. Pac-Man vs. Ex-Aid & Ghost with Legend Rider

"Tricks": Kamen Rider Genm

Collabos Bugster in his prime body reemerged with Proto Gekitotsu Robots and Proto Giri Giri Chambara installed. After quick battle with Emu, who used Kaigan Ghost, Full Throttle Drive and Toukenden Gaim Gashats, he falls on the hands of Kamen Rider Genm, who uses the power of the Legend Rider Gashats to complete his Ganbarizing Gashat. Using the blank Collabos Bugster as a conduit to harness the power of Kamen Rider Battle: Ganbarizing, a game Emu is unfamiliar with, Genm brings forth manifestations of Kamen Riders Double, OOO and Fourze. Part. I: Legend Rider Stage

Team of Bugster viruses appeared in the Game Area of Famista where they encounter Brave acting as baseball pitcher. Back in the real world, Poppy Pipopapo discovers the inert Collabos Bugster which she is unable to budge, projecting a blank Game Area which soon enough manifests as Ganbarizing, causing it to come back to life and go berserk before Ex-Aid arrives, allowing Poppy to get away. Taking out the Ganbarizing Gashat from the Bugster's head, Ex-Aid inserts it into his Gashacon Breaker, performing its Critical Finish to destroy the Bugster. Part. II: Legend Gamer Stage

Major Bugsters

Minor Bugsters


Other Bugsters


Main article: Collabos Bugster

Main article: Bugster Union


  • The Bugster virus was caused by the Y2K event, the real-world prediction that computers' 2-digit year displays becoming "00" for the year 2000 would cause all computers in the world to stop working properly, as they may believe the year to be 1900 instead. In reality, at least in part to preventative measures, very little happened.
  • All Bugsters are designed by Katsuya Terada who is well known for designing the Dopants.
  • The Bugsters being genetic viruses given humanoid form is reminiscent of the Amazonz, especially when they begin to spread out as seen with the sequences shown.
  • The virus effectively replacing the host, assuming a large form before taking on a more humanoid frame, is reminiscent of the Phantoms of Kamen Rider Wizard
    • Unlike the Phantoms, however, the virus does not necessarily use the original body when the virus claims the infected host, such as the case of Graphite's host being different from the human form it currently possesses.
    • But the way they are cultivated with their cultivators working in pairs is similar to the way the Makamou are cultivated.
      • An exception to this rule is the Level 30 Bugsters, where they not only cultivate their hosts but also possess them. And upon defeat, the Bugster Viruses would eject from the host's body similar to the Dopants of Kamen Rider W having their monstrous Gaia Memories destroyed.
  • Given the series' gaming motif, the revived Bugsters altered appearance and additional abilities is likely a reference to enemies becoming more powerful and possessing new or enhanced abilities at higher difficulty levels.
  • Bugsters' weapons possess their owner's name: ex. Salty Bugster's Salty Knuckle.
  • Bugsters using Kamen Rider Chronicle to commit genocide on humanity and become the superior race on Earth mirrors the goal of the Orphnochs working for Smart Brain in Kamen Rider 555.



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