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

Sento and Ryūga awaken from a strange dream in which Sento seemingly extracted Ex-Aid's power. They are alerted to a Smash attack, but the threat proves to be Bugsters that resist their attacks. Sento uses the newly created Doctor and Game Fullbottles to transform into Ex-Aid.

A blue-armored figure named Kaiser appears and steals the Fullbottles. Sento retrieves them, while Ryūga is dragged into a machine that sends him to a parallel world where the Skywall does not exist.

Sento's world shifts between dimensions, spreading hordes of Bugsters in both worlds. Emu is unable to transform into Ex-Aid, so the other Riders take the initiative to fight the Bugsters.

Kaiser Reverse launches an attack on Emu's group but is driven off by Kamen Rider Ghost. He reveals that their world will be destroyed in 24 hours, setting a ticking countdown for the battles ahead.

Parad confronts Sento, claiming two years of searching for Build to restore Ex-Aid's essence. Sōichi intervenes and identifies Kaisei Mogami as the culprit behind Enigma. Parad uses a Game Fullbottle to contact Emu, and Sento receives Phoenix and Robot Fullbottles from Sōichi.

Kuroto develops a new Gashat using data from his earlier fight, and Onari pressures supplying more power for the Doctor Riders. Sento and Sawa uncover Mogami's past: he worked under Takumi Katsuragi on Enigma and synthesized Nebula Bugsters by exposing them to Nebula Gas.

Sento realizes Takumi stole Ex-Aid's powers to prevent them from being sealed, a countermeasure against Enigma. The revelation leaves him puzzled about how the dream-related event fits into reality.

As Nebula Bugsters threaten the population, Kaiser attempts to stop them but is driven back by Build PhoenixRobo Form. The Riders rally as the Nebula threat escalates.

Sento and Parad locate Kaiser's hideout with Misora's help. Sento concludes Takumi's aim was to prevent the Bugsters from being sealed, and the group prepares for a direct confrontation.

A new Build Gashat is created by Kuroto, and Taiga, Hiiro, and Kiriya join Takeru against the Nebula Bugsters. A cliff opens and Ryūga nearly falls, but Eiji Hino arrives to help rescue him.

Eiji reveals Foundation X is working with Mogami on Enigma, and the trio sets out to confront him at his base. Sento confronts his world's Mogami, who becomes a cyborg after Takumi's attempt to stop him.

Mogami is joined by his dimensional counterpart, and the two reveal their plan to cause a convergence between the worlds to become Bi-Kaiser. Bi-Kaiser uses Core Medals to create replica Greed and restore Eiji's ability to fight by reviving Ankh as Kamen Rider OOO.

Kamen Riders Fourze and Gaim join Sento and Emu as they reach the Enigma machines on both worlds. They resolve to prematurely activate Enigma with Bi-Kaiser's power at only a fraction to restore Emu's powers.

Build and Ex-Aid confront and destroy Bi-Kaiser along with the Enigma machines, stopping the convergence. The dimensional barrier is restored and the Riders part ways, with peace returning to their respective worlds.

In the post-credits scene, Sento and Ryūga confront Guardians from Faust. A mysterious Rider steals the Phoenix and Robot Fullbottles, claiming they belonged to Hokuto and vows to return.