The Crisis Empire lays an intricate trap for Kotaro Minami, the heroic warrior known as Kamen Rider BLACK RX. By manipulating time itself, the villainous organization sends Kotaro back to an earlier period, forcing him to relive a past conflict. Upon arrival in this displaced timeline, Kotaro finds his power set has reverted, transforming him back into the original Kamen Rider BLACK, a less advanced form than his current RX state. He soon finds himself cornered by the priests of Gorgom, the sinister cult he had previously defeated, and is captured.

However, the Crisis Empires scheme has an unforeseen consequence. The act of sending Kotaro through time splits his persona. The modern RX consciousness does not travel with his captured past body. Instead, RX materializes separately in the same era, fully aware of the trap and determined to rescue his former self. As BLACK struggles to survive against the Gorgom priests, BLACK RX arrives to intervene. The battle escalates, forcing the Crisis Empire to deploy more forces. To counter this threat, Kotaros other specialized forms also manifest: the fluid-based Biorider and the heavy-combat Roborider, each an extension of Kotaros own will and power. Together, the four distinct versions of Kotaro Minami unite on the battlefield, combining their strength to confront the Crisis Empire and undo the temporal trap that threatens to erase the future.