The bugster Virus, formed from video games, threatens humanity and seeks to turn Bugsters into complete beings. A hospital intern, Emu Hojou and three other Kamen Riders (Brave, Snipe and Lazer) must defeat the virus and save humanity.

5 years ago, a new type of virus, named the Bugster Virus, infected humanity and turning them into a creature called a Bugster. In the present day, an intern and also a genius gamer, Emu Hojo receives the Gamer Driver and the Mighty Action X Gashat to transform into Kamen Rider Ex-Aid. Along with several doctor Riders, Emu must compete to save people from the Bugster Virus and become the "super doctor" who'll save humanity! GAME START!