A cosmic event involving an artifact like cube crafted by an ancient Martian civilization has created a supernatural barrier called the Sky Wall, which divides future Japan into three literal, and figurative regions, Touto, Hokuto, and Seito. Along with creating a complex split between the three, the event has brought with it legions of creatures dubbed Smash down onto the country, who chase and attack citizens on sight. Sento Kiryu, having lost his memory, is found and sheltered by a enigmatic cafe owner named Soichi Isurugi who gives him a belt called the Build Driver that gives him the ability to turn into Kamen Rider Build, which he uses to fight the Smash in his own way. Sento learns that his forgotten past is connected to the events of the Sky Wall Disaster. In his search for the truth about his past and a solution to the current crisis, Sento makes several friends who also gain the ability to transform and battle with him, acquires several adversaries who fight back at his attempts to save everyone, and is pushed to figure out who is on what side, and what the sides even are or mean! Fan adapted Novel following the Show "Kamen Rider Build" as closely as possible.