Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider

Lore & Background

The film follows Sento Kiryū and Ryūga Banjō as they encounter Bugsters immune to their attacks, leading Sento to use newly created Doctor and Game Fullbottles to transform into Kamen Rider Build's Ex-Aid Hazard Form. A blue-armored figure called Kaiser steals the bottles, and Ryūga is thrown into a machine that sends him to a parallel world without the Skywall. The worlds shift between dimensions, spreading Bugsters in both, while Emu Hojo cannot transform into Ex-Aid. Bi-Kaiser appears, revealing that the Bugster epidemic fuels his machine Enigma, which seals the powers of all Heisei Riders. Kamen Rider Ghost intervenes, warning that their world will be destroyed in 24 hours.

Reader's Guide

The film is significant as a crossover event that brings together characters from multiple Kamen Rider series, including Build, Ex-Aid, OOO, Fourze, Gaim, and Ghost. It introduces the villain Kaisei Mogami, a researcher who developed the trans-dimensional machine Enigma and the Kaiser System, synthesizing Nebula Bugsters by exposing the Bugster Virus to Nebula Gas. The plot involves a convergence of parallel worlds, with the heroes working to stop Bi-Kaiser, a merged form of Mogami and his dimensional counterpart. The film earned $10.2 million at the Japanese box office and was released on DVD and Blu-ray on May 9, 2018. A tie-in web series, Legend rider in 3 minutes, was released on Toei's official YouTube channel to introduce returning characters.

Did You Know?

• The script was co-written by Shogo Muto and Yuya Takahashi, the head writers for Kamen Rider Build and Kamen Rider Ex-Aid respectively.
• The film features a medley of opening theme songs from Kamen Rider Build, Ex-Aid, Ghost, Fourze, Gaim, and OOO as its theme song.
• The villain Bi-Kaiser uses Core Medals developed by Foundation X to create replica Greeed.
• In the post-credits scene, a mysterious Rider steals the Phoenix and Robot Fullbottles from Sento, claiming they are from Hokuto.

The Convergence Crisis

The narrative architecture of this 2017 crossover film is built around a dual-dimensional threat. A trans-dimensional machine known as Enigma operates in parallel worlds, functioning as a mechanism that seals the powers of both Gamer Drivers and Gashats. The Bugster epidemic that plagues these dimensions is not merely a nuisance but the very fuel that powers Enigma. When Sento's reality begins shifting between dimensions, hordes of Bugsters spread across both worlds simultaneously, and Ryūga is flung into a parallel dimension where the Skywall does not exist. The stakes escalate sharply when Kaiser Reverse reveals that the Bugster outbreak is intentional infrastructure feeding the Enigma machines. The resolution demands a coordinated strike: the heroes must prematurely activate both Enigmas while their combined enemy, Bi-Kaiser, is reduced to a fraction of his full power. This allows Emu's abilities to be restored and the machines to be destroyed, ultimately restoring the dimensional barrier and halting the convergence that would have merged the two worlds into one.

The Legend Riders' Return

Four veteran Riders from earlier Heisei entries—OOO, Fourze, Gaim, and Ghost—step in to support the Build and Ex-Aid casts during the convergence crisis, each bringing a distinct contribution to the unfolding battle. Kamen Rider Ghost arrives at a critical moment to drive off Kaiser Reverse and delivers the grim intelligence that Emu's world faces destruction within twenty-four hours. Eiji Hino materializes to pull Ryūga from the edge of a sudden cliff opening, then discloses that Foundation X in his dimension is collaborating with their local Kaisei Mogami to build their own Enigma. During the final confrontation, Eiji deploys an Ankh clone to resurrect the original Ankh, reclaiming his capacity to fight as OOO. Fourze and Gaim assist Sento and Emu in reaching the Enigma machines on their respective sides of the dimensional divide. In the aftermath, Onari is welcomed back to the Daitenkū-ji temple, and Ankh's vessel slowly fades, with Eiji vowing they will cross paths again.

The Kaiser Fracture and Its Architects

The antagonistic structure of the film is layered across dimensions. A blue-armored figure designated Kaiser appears in Sento's world, while a red-armored counterpart called Kaiser Reverse operates in Emu's. Both are connected to Kaisei Mogami, a researcher who once published work on developing the Enigma trans-dimensional machine and who previously worked under Takumi Katsuragi. Takumi's role is revealed as more sympathetic than villainous: he extracted Ex-Aid's essence as a defensive countermeasure to prevent those powers from being sealed by Enigma. Mogami, however, pursued a far more destructive path—he synthesized the Nebula Bugsters by exposing the Bugster Virus to Nebula Gas and developed the Kaiser System. Parad, who spent two years searching for Build in his own world to recover Ex-Aid's essence, adds another layer of motivation. The ultimate threat emerges when Mogami and his dimensional counterpart merge into Bi-Kaiser, a god-like entity wielding Core Medals from Foundation X to generate replica Greed and overwhelm the assembled Riders.

Threads Beyond the Final Battle

While the film concludes with the destruction of Bi-Kaiser and the restoration of the dimensional barrier, several narrative threads extend well beyond that final confrontation. In the post-credits sequence, Sento and Ryūga encounter a group of Faust Guardians when an unidentified Rider materializes, snatches the Phoenix and Robot Fullbottles from Sento, and declares that those Bottles originally belonged to Hokuto before vanishing with a promise of his return. This teases future conflict and recontextualizes the Fullbottle's ownership. On the Ex-Aid side, Kuroto Dan leverages data from his earlier clash with Build to engineer a new Gashat, enabling him to briefly recover his powers, and is persuaded by Onari to produce additional Gashats for the other Doctor Riders. Sōichi entrusts Sento with the Phoenix and Robot Fullbottles after Parad's intervention. These details suggest the film functions not as a definitive endpoint but as a pivot point, leaving multiple character arcs and power dynamics deliberately unresolved for the broader Kamen Rider franchise to continue exploring.