Professor Daidōji has developed a gravity machine called the GX Device. Unfortunately, Shocker wants it; so they attack the professor and destroy his laboratory, but come home empty-handed. Shocker's agents find out that the plans for the GX Device are with Daidōji's daughter, who is celebrating her birthday. Now the Kamen Riders, along with FBI agent Kazuya Taki, must protect Daidōji's daughter and prevent Shocker from obtaining the plans.

Takeshi Sasaki
as Hayato Ichimonji / Kamen Rider #2

Hiroshi Fujioka
as Takeshi Hongo / Kamen Rider #1

Akiji Kobayashi
as Tobei Tachibana

Jirô Chiba
as Kazuya Taki

Hideyo Amamoto
as Dr. Shinigami

Wakako Oki
as Yuri

Emily Takami
as Emi

Yoko Sugibayashi
as Mika

Yasuharu Miura
as Goro

Hajime Izu
as Dr. Daidōji