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.