Watch Online Free on Watchseries. The Crisis Empire devise a plan to defeat Kotaro Minami by reverting him back to his old form of Kamen Rider Black and sending out several revived monsters after him. However, Kamen Rider Black is assisted by another RX, who used a time warp to help his past self. The two are joined by RX's alternate forms of RoboRider and BioRider and the four Kamen Riders combine their powers to defeat the revived monsters.