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.

Emu follows a patient who’s fled in fear of a doctor and encounters Taiga, who transforms into Kamen Rider Snipe. Once Emu learns of the past connection Taiga had to CR, he visits the dark hospital Taiga resides in to rescue the patient.

Emu cannot transform into a Kamen Rider since Taiga stole his Gashat. Medical Examiner Kiriya Kujo appears before a crestfallen Emu. He brings a Bugster-infected patient and offers to steal back Emu's Gashat in exchange of helping Kujo out with his prodigious gaming abilities.

When the thief of the 4 new Rider Gashats is infected with the Bugster virus, Emu and Hiiro clash about saving his life or not, and the identity of the mysterious Kamen Rider that is attacking the others is finally revealed.

The girlfriend of the student that the Bugsters were after has contracted the Game Disease. Hiiro transforms into Brave and succeeds in separating the Bugster from the girl.

A hospitalized patient showing two symptoms of the Game Disease has appeared. Emu and Hiiro transform and succeed in separating the two Bugsters from the patient. But Genm appears again to interfere, letting the Bugsters escape.

Taiga manages to capture the Bugster which escaped in the last episode and obtains the Jet Combat Gashat, holding the Bugster, and thus the patient, hostage in exchange for the other Riders' Gashats. When they arrive to challenge him, he decides only he is needed to fight the Bugster, and tries to destroy Ex-Aid and Brave.

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.

Emu gives Kiriya another chance to earn his trust. Kiriya then takes the chance to finally reveal Kuroto's intentions and expose him as the Black Kamen Rider that is working with the Bugsters.

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…

Ex-Aid, now as two, get into an argument about defeating Genm or the Aranbura Bugster. They both seem to be Emu, but Genm and the Bugster take this opportunity to escape. Emu reverts to his human form and falls unconscious. Wanting to save Dr. Shirakawa, Emu asks Hiiro to perform a surgery on his cancer. He has his Gashat back and faces the Aranbura Bugster to also cure Shirakawa's game illness. Will the surgery succeed? What will happen to Ex-Aid?!

Taiga tries to find out more about Emu's infection, and starts to discover the secret that might be why Kiriya was killed. Meanwhile, using data collected from fights with Mighty Brothers XX, Parad makes his move and reveals his new form: Kamen Rider Para-DX Level 50.

Emu thinks Taiga and Hiiro attacked him since he is the source of stress for Nico, who is suffering the Game Disease. He does not realize the true intention of the other two riders is to eliminate the Bugster virus residing in Emu himself, who is unknowingly infected with the disease as well. Brave attacks Ex-Aid again but Revol Bugster and some grunts appear to…defend Emu! He is further convinced he is the source of Nico’s stress. Genm Level X appears and attacks both riders. He succeeds in stealing all of Hiiro’s Gashats and seems intent to do the same with Emu’s.

A lovable hamburger Bugster named Burgermon appears. Emu transforms into Ex-Aid, but attacking it causes the game disease patient to suffer from stress. What is this? The CR accommodates an employee of the Genm Corporation’s development department. A game called Ju Ju Burger is under development with a game virus infection, and Burgermon seems to be separated from the game. Burgermon acts like an adorable child; he doesn’t seem so bad. As expected, Emu will have to deal with what’s in control of his head.

"Hiiro, are you hiding something from me?" Emu calls out Hiiro on the roof of the hospital. In the last battle, Genm tells Emu that he saved the Bugster because his body told him to do so. Emu also suffers from serious headaches after every transformation since creating the Mighty Brothers XX Rider Gashat. And most of all, Emu is incompatible with the surgery and yet he can still transform into a Kamen Rider. Everything is starting to come together, so what will Hiiro's response be? Meanwhile, Kuroto Dan returns to Genm Corp., and using the Gashacon Bugvisor, he begins to spread the Bugster Virus...

Emu finally learns of the horrifying truth that he has the game illness. The Bugster virus in him acts up and he collapses to the ground, though for some reason no Bugster has appeared... Emu later wakes up in CR with his personality completely changed to that of "Genius Gamer M". When a new Level 30 Bugster emerges, Emu transforms into Ex-Aid with delight, and fights as if he were playing a game while no longer concerning himself with the patient. Just what has happened to Emu?

Taiga and Nico meet a high school student named Daisuke who is infected with the Bugster Virus and calls both Emu and Hiiro for their help. Parado suddenly appears and Hiiro faces him in his new form while Emu is hesitant on joining the fight.

Emu and Hiiro learned from Poppy that Kuroto was the one who had suggested Emu to CR. Meanwhile, a police detective is investigating the Zero Day case, causing him to interrogate Kuroto's father, Masamune. During the investigation, he gets infected by the Game Illness. In order to save him, Emu confronts Masamune.

Kuroto falls victim to the Bugster virus and is aprehended by the authorities. Despite everything Kuroto did to him and his friends, Emu is determined to treat him, but the others are wary, wondering if saving Kuroto's life is worth the effort, or even if he will be grateful for it. On the other sides, Hiiro finds some very useful information from Kiriya Kujo's belongings while Emu receives an emergency call that a Bugster is rampaging on a certain location.

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.

The fierce battle between Ex-Aid and Genm has now come to an end. Meanwhile, a woman who was injured, Sora, is brought to Emu and Hiiro. Sora's band members argue, when suddenly all 3 of them are taken over by Bugsters! And on top of that, when Emu tries facing them alone, a young man appears yelling, "Yossha Lucky!"

Recently, Emu has been feeling a little worried. He is very quiet and hasn't talked much since Poppy Pipopapo suddenly disappeared. Just then, Hiiro is shocked by the sheer number of emergency calls coming to CR, all reports of the game illness! As the only CR doctors, Emu and Hiiro rush to the indicated locations, but what they find there is an unbelievable sight...