Emu, a clumsy pediatrics intern takes young Sota, who is suffering a mysterious illness, to the announcement event of the latest "Mighty Action X", Sota's favorite game. Emu became a medical doctor in order to save someone's life because his life had been saved once through surgery.

However, a mysterious virus emerges from Sota's body and the event turns into chaos. Emu hears from Asuna, an employee of the Ministry of Health, that transforming into a Kamen Rider can save the patient. Emu takes on this "operation" and inserts the Mighty Action X Gashat into the Gamer Driver, transforming into Kamen Rider Ex-Aid!

Becoming Kamen Rider Ex-Aid, Emu now must serve as both a pediatrician and a member of CR. A gifted surgeon named Hiiro Kagami comes back from the United States and is not only the son of the director, he’s also Kamen Rider Brave. This results in a clash of ethics when it comes to dealing with patients.

Graphite infects the Deputy Director-General of the Ministry of Health with the Bugster Virus, while the doctors at the CR fall out over the most important course of action: Save the Patient or defeat Graphite?

Unable to control the powers of the new "Drago Knight Hunter Z" Gashat only by himself, Emu discovers that to do so he must convince the other Kamen Riders into join forces with him. Once he tricks them into doing so, the time comes for their showdown with Graphite.

With Christmas around the corner, Emu runs against time to defeat the Salty Bugster again and save another patient, while Kiriya's investigation leads him closer to the truth, but his life is in danger when he faces Kuroto's new power.

With the Bugster infection spreading rapidly, the authorities can't hide the disease from the public anymore. After Kiriya's death, Kuroto starts targeting the other Kamen Riders for their Gashats, but Parad approaches Emu, offering him a blank double Gashat which will allows him to attain a new level of power…

Recovered from his infection, Kuroto resumes his plans to complete "Kamen Rider Chronicle" and the members of CR seem to have no way to stop him, until Taiga gives Emu a new Gashat that brings forth a power never seen before.

Kamen Rider Chronicle has already begun! Para-DX has joined the game and defeated the first round of the general players, giving them a Game Over as Emu watched them disappear before him. Kamen Rider Chronicle is being sold at an extremely fast rate, which catches the attention of the Ministry of Health. To avoid any form of confusion, Kyotaro Hinata orders a temporary halt on the actions of the doctors in CR. However, a game disease patient escapes from CR in an attempt to cure his own game disease, which leads Emu to chase after him. Then suddenly, Poppy Pipopapo appears before them with a new Driver and a Rider Gashat of her own…

The Last Boss of Kamen Rider Chronicle, Gamedeus, is finally born! If you defeat Gamedeus, then the game will end! However, at the moment of Gamedeus' revival, massive amounts of the Bugster Virus spread throughout the city! The number of infected patients are increasing, as well as the number of people being rushed to the hospital. While the doctors attend to the patients, Ex-Aid and Para-DX team up to fight Gamedeus! But their strength is far too weak against Gamedeus, as he sends them flying easily. At the same time, two people were confronting each other. Kiriya and Kuroto, both transformed, clash fists to see who's fate will be decided in the end…

Though Gamedeus was finally destroyed at the cost of Poppy Pipopapo and Parado when they extracted the Bugster from his body, Masamune Dan survived and takes advantage of Emu no longer being able to use Hyper Muteki. The Kamen Riders are at a huge disadvantage, while Cronus doesn't hold back, and initiates Pause. All of the Kamen Riders' movements are frozen in time, and he prepares to kill them, starting with Emu…