|This article is about a/an secret plan in Kamen Rider Build.|
Project Build (プロジェクトビルド Purojekuto Birudo) was a series of top-secret research files compiled by Takumi Katsuragi on the creation of Rider System and its accompanying gear.
The idea was first conceived by Shinobu Katsuragi, who after the Sky Wall Disaster had discovered that Earth would come under attack by aliens known as the Blood Tribe After receiving his son's blessing and support, Shinobu began work on harnessing the Nebula Gas in order to develop the necessary weaponry strong enough to oppose Evolto. .
Shinobu's efforts to even try and fight against Evolto were noticed by the monster himself, which the latter asked him to restore the essences of the Fullbottles that Vernage drained in order to put his plans back on track. Attempting to defy his orders, Shinobu created the Build Driver and was forced to fake his own death to escape Evolto's demanding clutches. Takumi used his father's research and continued his legacy as a member of Faust. However, Takumi was unaware of the fact that his research was being manipulated into becoming weapons of warfare by Evolto himself, and secretly entrusted the remainders of his research to his mother when he found out.
Sometime later, Sento Kiryu and Ryuga Banjo visited Takumi's mother and retrieved the files. However, a copy of the Sclash System research blueprints were stolen and given to Nariaki Utsumi, which incited the Japanese Civil War.
Shinobu began to study the blank Fullbottles and discovered that the essences of the Fullbottles could take on the properties of two things: something biotic or abiotic. In his first attempt to defy Evolto, Shinobu created an experimental system of weapons that could harness the power of these bottles: the Rider System. At the very forefront, Kamen Rider Build was the main product of this series of weapons and the project's namesake.
The first Build Driver was created by Shinobu in his first attempt to create a "good" version of Evolto's Evol-Driver that was safe to use by humans, which he took with him as he faked his death and relocated to Seito. After Takumi completed his own construction of the Build Driver using his father's research, he recorded a video demonstration titled File 001 - Build, showcasing Build's combat capabilities against two Guardian.
Takumi's Build Driver was later inherited by Sento, with Sento later building one for Ryuga Banjo.
As a result of the new world, Sento was also able to use the Build Driver schematics to recreate a safe and humane version of the Evol-Driver for Nariaki Utsumi.
In retrospect to the people unable to survive a Nebula Steam transfusion, Takumi created the Transteam Gun to allow those individuals to transform without the risks of being exposed to any Nebula Steam. The resulting transformation is a suit of armor safely created without the dangers of Nebula Gas exposure. The system includes a voice modulator to give the user some level of privacy protection. Takumi had two guns created, one each for Soichi Isurugi and Gentoku Himuro.
In the video demonstration Takumi recorded under the name File 002 - Blood Stalk, he stated that the Transteam system was created to push Build's growth potential further, by challenging its limitations. These armors grant only an additional measure of defense, while its offensive capabilities depend solely on the users.
Upon Sento accessing File 00X - Sclash, Takumi congratulated him as he unveiled his latest and greatest protect: the Sclashjellies, jelly-pack like containers that contain Fullbottle essence, solidified as gel. However, Takumi admitted that this technology was unfinished, and was only able to create Sclashjellies for two essences.
As Sento continued combing through Takumi's research, he discovered the Jellies were utilized by the new Sclash Driver, which none had existed then. When Soichi had originally stole a copy of the research from Sento, it was presented to Nariaki Utsumi, who then built a Sclash Driver from the schematics for Kazumi Sawatari, who transforms into Kamen Rider Grease. Sento then proceeded to build one of his own for Ryuga Banjo who transforms into Kamen Rider Cross-Z Charge. Later on in the war, Utsumi built one for Gentoku Himuro, who transforms into Kamen Rider Rogue.
At some point in the past, Shinobu discovered that Pandora Box housed the powerful Evol-Trigger, which was Evolto's catalyst for his Black Hole form and eventual monster form. To combat this, he created the Hazard Trigger, which had the ability to nullify the Lost Bottles that powered Evolto's monster form. It was originally meant to be used alongside the Pandora Box, or at least with one its panels (the Genius Fullbottle), otherwise using it with just the Build Driver and two bottles will pose a real danger to the user. It not only increases Build's power output dramatically, but prolonged usage will cause the user to induce a destructive impulse, due to the overwhelming stimuli being transmuted into the brain.
Takumi later discovered the existence of this and locked his video explanation of it behind a password, which was titled File XXX - Hazard Trigger. Later the Trigger went into the possession of Evolto, which he directed Sento to find the locked file and gave him the Trigger. At one point, Ryuga stole it for Kengo Ino before Sento defeated him and got it back.
At some point, Takumi began collaborating with Kaisei Mogami on his research of the Enigma, an inter-dimensional system that would allow him to travel between the World of Build and the World of Ex-Aid. Takumi used the portal to travel to Ex-Aid's world, where he thought he encountered Ex-Aid, later leaving and returning. On his final trip there, he met the genuine Ex-Aid and stole his powers.
After Kaisei Mogami returned and posed a threat to Sento, Sento discovered Takumi's files on Mogami and Ex-Aid's powers, including his trips there.
- Project Build itself is an ironic solution to fight Evolto, as most of the weaponry developed under Project Build had originated from Evolto's own property, the Evol-Driver and the Evol-Trigger.