This article is about a/an monster in Kamen Rider Ex-Aid.

A Bugster Union (バグスターユニオン Bagusutā Yunion) is the monster form of a Bugster-infected patient when the virus first flares up.


Bugster Unions are formed when a Bugster-infected patient experiences enough stress, the Bugster viruses inside multiplying rapidly and overtaking the patient's body, forming a giant orange virus form around it; the Union's shape seems largely irrelevant to the Bugster's appearance. Bugster Unions 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.

The Bugster Union stage is bypassed for Bugsters in Level 3 or more.


Salty Bugster Union

A golem-like Bugster Union emerges from Sota Suyama's infection, rampaging at the release event for the game Mighty Action X. It is defeated by Ex-Aid Action Gamer Level 1 using a Speeding-Up Energy Item and the Gashacon Breaker, releasing the Salty Bugster. I'm a Kamen Rider!

Aranbura Bugster Union

A bacteriophage/wall torch Union emerges from Rensuke Natori's infection at a public fountain, being fought by Brave and Ex-Aid Quest and Action Gamers Level 1. It is cut in half by Brave's initial sword, releasing the Aranbura Bugster. Another Prodigy with No Thank You?

Revol Bugster Union

A floating pistol Union emerges from Yuki Kitami's infection in a park, quickly being destroyed by Snipe Shooting Gamer Level 1's body-bullet attack, releasing the Revol Bugster. BANG, That Jerk is Coming!

Motors Bugster Union

A spiked wheel Union emerges from Yoshitaka Nishiwaki's infection, fighting Snipe and Lazer Shooting and Bike Gamers Level 1. It is destroyed by Lazer, releasing the Motors Bugster. An Operation Called Dash!

DoReMiFa Collabos Bugster Union

A floating aquatic creature Union emerges from Yoko Horiuchi's second infection, fighting and being defeated by Brave Level 1 with a rapid flaming attack, releasing the DoReMiFa Collabos Bugster. A Hollow Beating in the Heart!

Giri Giri/Jet Collabos Bugster Union

A massive two-headed Ouroboros serpent Union emerges from Yoshio Okada's double infection in the CR patient ward, fighting Ex-Aid and Brave Level 1 after being Stage Selected to a rocky shoreline. It is destroyed by the Riders, releasing the Giri Giri and Jet Collabos Bugsters. The Reason for Some Lies!

Hunter Gamer Union

A dragon Union emerges from Kyotaro Hinata's infection from the Proto Drago Knight Hunter Z Gashat, separating from him to form instead of taking him over. It easily overpowers Ex-Aid and Brave Level 1, growing stronger before being challenged by Snipe Combat Shooting Gamer Level 3, eventually being destroyed by Ex-Aid Action Gamer Level 2 with a dual Mighty/Taddle Critical Finish, releasing the pieces for the Hunter Gamer to complete the Drago Knight Hunter Z Gashat. Beat Up the Dragon!

The dragon Union is briefly resummoned by Genm Zombie Gamer Level X while using a dual Taddle/Drago Knight Critical Finish against Brave Fantasy Gamer Level 50, but it is easily destroyed by Brave's counterattack. A Sudden Fantasy!?

Combined Union

Genm Level X merged a horde of zombie Bugster Viruses into a Bugster Union form combined from the first several, with the body of Salty's golem, Aranbura's wall torch for a tail, Revol's pistol for a right hand armament, and a pair of Motors' spikes wheels for shoulder pads. It is destroyed by Ex-Aid Maximum Gamer Level 99 before being immediately reformed by Genm, but is reverted to the crowd of zombie Viruses by Maximum Mighty Critical Finish. Extreme Dead or Alive!

Gemdeus Bugster Union

Para-DX and Graphite went to the world of Kamen Rider Chronicle to obtain a virus sample of Gemdeus as a quick countermeasure on Cronus.Here they meets a sliver Bugster Union which appears to be Gemdeus itself, the Union rampages and kept attacks on the Bugster duo, until Graphite eventually obtain a sample with his Bugvisor and the duo leaves the game.


Behind the Scenes

Like most giant monster forms, all Bugster Unions are completely CGI. Likely as a result and to minimize the budget, Bugster Union battles are often short or the audience is given only a limited view of the action to reduce the Unions' onscreen time.


  • It's unknown how Ex-Aid was able to defeat the Dragon Bugster Union in Level 2 when Asuna Karino stated that a Kamen Rider can only defeat a Bugster Union in Level 1, though because it separated from the infected patient instead of consuming them, it may have been a different type of Union.
    • Alternatively, only defeating a Union in Level 1 may have been because stronger forms would risk injuring the patient trapped inside, and since the Dragon Union had no patient inside, there was no risk.
  • The nature of how to deal with the Bugster virus being dependent on its form is similar to how certain viruses require different procedures or methods of treatment even if similar in nature. If true, then the stability of Unions may be such that only the lowest levels are able to safely eliminate them without taking the patient with it.
    • This theory would explain how Bugsters of higher Levels pose less of a risk to the patient when using sufficient force to eliminate them, especially when possessing their bodies while active.