Before the Skywall Incident
- Killbas, the king of the Blood Tribe, destroys Planet Blood and orders the remnants of his race to destroy other planets. His younger brother, Evolt, survives and escapes with a power artifact that was made to destroy planets.
- The civilization on Mars creates the Pandora Box. In truth, it was created by the Blood Tribe, which comes from a planet far beyond our solar system. Evolt uses its massive power to destroy the entire civilization.
- As Mars is destroyed, Vernage, the queen of Mars, battles Evolt. Evolt’s Evol Driver and his body are damaged, but Evolt manages to survive by sealing himself in the Pandora Box. Vernage seals her own soul inside a golden bangle.
- An unmanned probe sent to Mars returns to Earth. Something inside enters Banjo's mother, and two months later, Ryuga, Evolt's Physcial half, is born. Takumi Katsuragi's father is assigned by Nanba to observe and check on him.
- Humanity finally lands on Mars and begins exploring it. One of the astronauts, Soichi Isurugi, finds Pandora's Box among the ruins of an very old civilization. Around this time Soichi gets possessed by Evolt's soul half and starts to develop powers like being able to reshape objects and faces. Soichi's memories are used to create the 60 Fullbottles within the Pandora Box.
- The other astronauts who explored Mars are similarly possessed by the souls of Evolt’s fellow Blood Tribe members. They return to Japan and become government officials.
10 years ago
- The mysterious Pandora Box is taken to Earth for Project Providence, hoping to advance Japan’s technology. But, on the day of launching, a security guard (Soichi Isurugi) activated the Box, causing the Sky Wall Incident that split Japan into three parts: Touto, Seito, and Hokuto.
- Elsewhere, Misora Isurugi has fallen into a coma because of the incident. In truth, she was looking at the recovered artifacts from Mars when she saw Vernage's bangle. Vernage took the chance to possess her and then used her power to empty out the essences of the Fullbottles within the Pandora Box, thus delaying Evolt's plans.
- Ryuga's parents die in an accident, leaving him orphaned and with vague memories of his past. His memories were wiped by Evolt, who also was the true cause of their deaths.
- Kaisei Mogami, a scientist of the Touto Institute of Advanced Matter Physics, studies the Sky Wall and publishes a research paper about the potential it holds for exploring parallel universes. While examining the Sky Wall’s extra dimensional properties, he discovers the Bugster virus native to the World of Ex-Aid.
- After being denied funding from the Touto Institute of Advanced Matter Physics, Kaisei Mogami takes his research to Namba Heavy Industries and invents a cross-dimensional machine called Enigma alongside his former supervisor and kindred spirit Takumi Katsuragi, intending to collect a larger sample of the Bugster virus from its universe of origin and experiment on it with Nebula Gas.
Between 10 and 7 years ago
Unknown- Takumi Katsuragi's father committed suicide because he was blamed for the Sky Wall Incident. In truth, it was because Evolt forced him to repair his Evol Driver. He faked his suicide and went into hiding.
- Touto came into the possession of Pandora's Box and put it in the Touto Institute of Advanced Matter Physics.
- Takumi joined the Touto Institute of Advanced Matter Physics to unravel the mystery of Pandora's Box.
7 years ago
Misora wakes from her inflicted coma and found a mysterious bracelet
with Vernage's soul inside on her left wrist. She also gains the ability to purify Smash essences.
Between 7 and 2 years ago
Unknown- Takumi Katsuragi established the organization, Faust, to research on Nebula Gas.
- Takumi created "Project Build" to utilize Nebula Gas for the purpose of creating an army of soldiers for Touto. He also completed the Rider system, with two pairs of Best Matches: RabbitTank and SmaphoWolf.
- Takumi is removed from the Touto Institute of Advanced Matter Physics because of his human experimentation.
- Misora is abducted by Faust.
- Later, Soichi Isurugi saved Misora from Faust, as well as plucking a panel of Pandora's Box, the Build Driver, and the Rabbit & Tank Fullbottles. In truth, took her out of Faust after she learned of its evil intentions and became unable to purify the bottles because of it, and he began his plan to get her to purify the rest.
Two years ago
- Mogami studies the Bugster virus native to the World of Ex-Aid and conducts experiments exposing them to Nebula Gas. Mogami's research brings about the creation of a new breed of Bugster virus foot soldiers called Nebula Bugsters. The essence of Nebula Bugsters serves as the fuel source for the completed Enigma and the Kaiser system.
- Katsuragi invents the Transteam Gun based off of the design of the Kaiser system’s Nebulasteam Gun, only simplified to operate purely off of Nebula Gas without the Bugster virus. The Transteam Gun becomes the basis for the system that allows Night Rogue and Blood Stalk to transform, the latter having been designed by Katsuragi to act as a rival that will motivate the Build Driver’s user to increase their Hazard Level.
- Kaisei Mogami uses the Enigma and makes contact with his own alternate counterpart from the World of Ex-Aid, who is a researcher for Foundation X. An accident with the Enigma caused when he got into a fight with Katsuragi causes serious injury to half of Mogami’s body, which must be modified with cybernetics.
- Using the Enigma, Takumi Katsuragi as Kamen Rider Build visits the World of Ex-Aid to collect a sample of Ex-Aid’s essence into a Fullbottle. He encounters Kamen Rider Genm in the midst of a Bugster virus outbreak caused by Gamedeus Cronus and mistakes his Action Gamer Level 0 form for Ex-Aid's Action Gamer Level 2 form, attacking him and accidentally killing off one of his ninety-nine extra lives. Build recognizes his mistake and takes his leave after Kuroto Dan SHIN rises from a CONTINUE pipe with three lives remaining and announces himself as god. Unbeknownst to Build, this encounter provides Kuroto with the battle data and inspiration to create a new addition to his collection of Legend Rider Gashats, a game called Kamen Rider Build.
- After Build's initial trip to the World of Ex-Aidnote an unknown amount of time after the first visit from the perspective of the World of Build's timeline, approximately one year after the first visit in the World of Ex-Aid's timeline, he returns and meets Emu Houjou and Parado, who are fighting Bugster foot soldiers in their Ex-Aid Double Action Gamer Level XX forms. Parado as Kamen Rider Para-DX is defeated by Build, who proceeds to harvest a sample of Ex-Aid's essence from Emu into a Legend Rider Fullbottle, robbing Emu of his ability to transform. Build returns to his homeworld, but will only recall these visits as hazy dreams once he becomes Sento and takes up the name of Build under that new identity.
- Parado chases Build to retrieve Emu's powers and follows him through the Enigma, landing in the World of Build. Parado will spend the next two years wandering about this world searching for Ex-Aid's powers, but only one week will have passed between his departure and actually finding Build from the perspective of the World of Ex-Aid's timeline.
One year ago until present time
- Takumi went to Hokuto and gave his mother the data of Project Build.
- Taro Satou, a guitarist for band "Lynk" helped his junior by working at a drug test for Takumi Katsuragi.
- Ryuga Banjou is accused of cheating at a mixed martial arts match and is banned.
- Kasumi, Ryuga's girlfriend, gave him a job at Takumi Katsuragi's house. He arrived one hour after Taro's arrival, but instead he found that Takumi is already dead. He was captured and convicted as the murderer.
- Taro Satou is experimented by Faust, but somehow escaped.
- Soichi Isurugi found an amnesiac Takumi at an alleyway. He gives him a new name, "Sento Kiryu" and guides him to become Kamen Rider Build.
- The above except for the first two items turns out to be false. In truth, Takumi called out Soichi and Ryuga after finding out they were both the two halves of Evolt. Unfortunately Soichi anticipated this and switched Takumi's Build driver with the prototype. Soichi then knocks out Takumi, murders Satou and uses his matter manipulation powers to switch their faces. He then called the cops to set Ryuga up. He then erased Takumi’s memories before experimenting on him and setting him up at the alley.
- Kamen Rider Build started his career, and the gossips of his appearances circulating on Touto’s citizens.
- Sento builds the purifier machine to assist Misora at purifying Smash essences without lapsing into week-long comas afterwards. Unknowningly, he used the Evol Driver as the power source for the machine.
Present time
- Ryuga Banjou is abducted by Nabeshima at prison, then is experimented on by Faust. He somehow escaped and met Sento Kiryu. Sento saved him from the pursuers, and they went to nascita to investigate the truth of Takumi Katsuragi's death.
- The existence of Kamen Rider Build is now publicly known by Touto government and Faust.
