As a child, Emu had a fascination with video games, thanks to his head doctor when he was a child giving him a portable console to play while he healed from a surgery. He particularly loved the game Mighty Action X, so much as to send in the concepts for a sequel game of his design. To his surprise, he got a demo of a working copy of his game as thanks, though he was unaware that he was infected with the Bugster Virus, becoming the first person ever infected by it. This virus would manifest in him as he grew, making him cockier, leading to him joining the competitive gaming scene. He adopted the moniker Genuis Gamer M, and quickly climbed the ranks. 


It was his biggest win yet, against the up and coming star N, that his Virus fully matured. Against his will, he was kidnapped, and the Bugster Virus was separated from him, manifesting into the entity Parad. However, the outbreak of Bugster from the separation was so strong that it infected his surgeons, and made them disappear, turning into Bugsters themselves. Emu, however, lived his life none the wiser, focusing on school to become a doctor, now that his former self had been restored. He eventually did test in as a pediatric intern, though he got caught up in something bigger when one of his child patients was infected by the Bugster Virus.


He learned of the CR, a center designed for Kamen Riders to combat the Bugster Virus, hidden in the hospital he worked in, and was asked to watch over his patient and prevent him from being stressed out. He decides to take his patient to the official release of Mighty Action X, as it was his patient's favorite game, but Asuna, the CR nurse, finds them and scolds Emu, stressing the patient out. This causes the Bugster Virus to outbreak, and it rampages. Emu takes chase, but Asuna reveals an alternate means: she intends to use the Gamer Driver she had with her to beat the Bugster. Emu takes it instead, and despite not knowing if he was compatible or not, assumes the role of Kamen Rider Ex-Aid, his M personality making a return. He beats stage 1 of the Virus, and it manifests into the boss of Mighty Action X, Salty, who he defeats by jumping up to level 2. Asuna finds out his identity as M, and he defeats Salty, curing his patient.


Later, in the CR, he learns that Asuna is actually the game character Poppy Pipopapo, from the game Doremifa Beat, and she gives him the challenge of beating the ten games. Mighty Action X is beat, but he still has Taddle Quest, Bang Bang Shooting, Bakusho Bike, Gekitotsu Robots, Doremifa BEat, Jet Combat, Giri Giri Chanbara, Shakariki Sports, and Dragon Knight Hunter Z.


Later that week, another patient is brought in, and Emu meets the genuis surgeon Kagami Hiiro, also known as Kamen Rider Brave. They work together to cure the patient, but are interrupted after beating stage 1 by a color-swapped Ex-Aid, who attacks them with a strange weapon. Regardless, the operation continues, and Hiiro defeats Alhambara, clearing Taddle Quest in the process.


The next patient is infected by the Bugster Revol, and Emu is introduced to the former radiologist Hanaya Taiga, also known as Kamen Rider Snipe. Taiga tells them he's the only Kamen Rider needed, and challenges M to a duel: the one who beat Revol gets the other's Gashat. Taig ends up winning, and confiscates Mighty Action X from Emu, as well as clearing Bang Bang Shooting.


When the next Bugster, Motos, infects a patient, the team runs into the coroner, Kujo Kiriya, also known as Kamen Rider Lazer. He challenges Snipe to get Mighty Action X back, but instead steals it when Brave and Snipe begin to duel, returning it to Emu so he can use Bakuso Bike to its full potential. They beat Motos together, clearing the game, but are attacked by the black Ex-Aid, who uses the Shakariki Sports Gashat to assume level 3. They are defeated, and the black Ex-Aid disappears.

The rpesident of Genm Corperation, Dan Kuroto, contacts CR, saying that 4 new Gashats had been completed, but were stolen. When Emu comes across a patient, he ends up being the Gashat thief, though he gets away when the black Ex-Aid, with the Gekitotsu Robots Bugster, attacks Hiiro and Emu again. Later, when confronted, the thief reveals himself to be the Bugster Graphite, born when Hiiro's girlfriend succumbed to the Virus and died. The four riders are attacked by him and the black Ex-Aid, and are losing until Emu finally morphs and challenges Genm to a duel, but instead defeats the Gekitotsu Bugster and uses the Gashat to assume level 3, beating the black Ex-Aid.


In later days, the other riders gain level 3 Gashats, Hiiro makes Graphite retreat by using Doremifa Beat, and Taiga manages to steal Gekitotsu Robots and Doremifa Beat when he gets Jet Combat. Kiriya, already not trusted for lying to Emu about a dead friend before, earns the trust of Emu again, and he gains the Giri Giri Chanbara Gashat from under the black Ex-Aid's nose. He then calls out the black Ex-Aid, pronouncing him as Dan Kuroto himself. However, when he defeats the black Ex-Aid, Parad ends up being in the form instead, and disappears after saying it was fun. Because of that, the team loses trust of Kiriya again.


When the head of the Ministry of Health, and Emu's idol, is infected, Emu is given the Gashat for Drago Knight Hunter Z, and was asked to defeat the mighty dragon to complete it, so him and his team could use the Gashat together. Instead, he acts selfishly, completing it alone, and assumes Level 5 to fight Graphite. However, he loses control, and rampages.


Later on, his M side takes over, and challenges the other 3 riders to a duel to see who would get the Gashat. However, in his defeat, he instead reveals that the Gashat splits into 4 separate ones, and they work together to destroy Graphite.


Confrontations with black Ex-Aid and orders to clear Shakariki Sports lead to the defeat of the black Ex-Aid, who names himself Kamen Rider Genm and reveals himself as Dan Kuroto. He absorbs data of death from his empty rider gauge, and seemingly finishes a new Gashat. The Rider team, now all working together, plan to defeat his as soon as possible.


However, on Christmas Day, after assuming Sports Gamer Level 3 and defeating the Bugsters, the team runs across Kiriya fighting a now-level 10 Zombie Gamer Genm, using the Dangerous Zombie Gashat, and cannot stop him as he defeats Lazer, causing a game over for Kiriya, killing him. Before he dies, he gives Emu Bakuso Bike and his Driver, telling him to change the patient's fate with his own hand.


The death of Kiriya hits Emu hard, and he vows vengeance on Genm, though none of them can best level 10. However, Parad approaches him with a blank Gashat, and Emu uses it to try and combat Genm. However, it infects him with a large quantity of the Bugster Virus. However, he instead channels it into the Gashat somehow, and creates Mighty Brothers XX, much to Genm's displeasure. With this, he assumes Double Action Gamer Level 10, and pummels on Genm, before assuming Double Action Gamer Level XX, splitting into two halves, Emu and M. The two argue over defeating Genm or the Bugster, allowing them time to escape. 


They later defeat Genm for the first time, as well as cure the patient. Parad reveals his affiliation with Genm, and his desire to beat Emu. Parad then assumes Puzzle Gamer and Fighter Gamer level 50, and beats the three Riders. 


The Juju Burger Gashat is created, and given to Emu to use to assume Burger Gamer LEvel 4, though it is stolen by Parad and Genm later on.


When Parad turns on Genm, asking him why he is needlessly killing Bugsters like him, Genm is defeated by the Bugster. In retaliation, Kuroto reveals to Emu that he is infected with Bugster Virus, and triggers a massive outbreak. However, Parad saves Emu from it by fusing with him once again, leading to M becoming the dominant personality. When Hiiro gains Taddle Fantasy, Emu once again regains control, tough he fears using Mighty Brothers XX.


More chains of events happen, with Genm gaining the power of level X, and he tells the riders of Kamen Rider Chronicle. To combat him, Taiga gets a blank Gashat, and installs Kiriya's DNA reprogramming research onto it. The Gashat is given to Emu in hopes that he can form a new game from it, and though he initially fails, when he is threatened, his Bugster Virus outbreaks again, and he forms Maximum Mighty X. He rewrites Genm's immortality, and knocks his Rider Gauge down, though he escapes. Later, he rewrites Genm's compatibility with Gashats, sparing him by stopping him from using Gashats. Parad, however, shows up, and infects Kuroto with Dangerous Zombie, killing him via Game Over.




Soon after, Parad finishes Kamen Rider Chronicle by taking Poppy, revealed as a Bugster, over, and the world falls into chaos. People assume the form of Ride pLayers, and fight both Kamen Riders and Bugsters. Emu watches Parad kill a group of humans, claiming that the game was made for the fight between Bugsters and humans. Parad reveals himself as Emu's Bugster and takes control of him, using him to torment the CR team.


Emu saves Poppy from Parad's control and grasp, adding Kamen Rider Poppy to their roster. She then remembers who she infected, and on following through, finds a level 0 version of Mighty Action X. Emu is shocked to find that, when he loses a decisive battle to Parad, Genm shows up, revived as a Bugster by Poppy. He has the power to nullify Parad's infection of Emu. The two clash, with Emu refusing to work together due to Kuroto's evil deeds, but they reach a concensus when Kuroto expresses interest in protecting that which he created. Ex-Aid and Genm both defeat Parad, with Genm getting Dangerous Zombie back.



Later that week, the decisive battle between humans and Bugsters begins, and it looks favorable. However, the battle is interrupted by Dan Masumane, Kuroto's father, who everyone thought he framed Zero Day on. Revealing he was the puppet master all along, he assumes the form of Kamen Rider Chronos, and defeats everyone.



From there, all Emu remembers is waking up in a new world.