After the defeat of Gorgom, Kohtaro is left homeless until he is taken in by the Sahara family. He became a helicopter pilot for the family's business due to their connections, beginning a new life for himself. Unfortunately, Kohtaro is later abducted into the Crisis Empire's mother-ship. The Crisis Empire was aware of his identity as Black and gave him an offer to join them. Kohtaro refused and fought back but was incapacitated when his transformation ability became disabled. He was ejected into space to float aimlessly until the sun's radiation altered his Kingstone. When his pod entered Earth's atmosphere, Kohtaro miraculously survives and immediately discovers he had gained a new power in the shape of an evolved rider form. With his new power, Kohtaro engaged the Crisis Empire forces as Kamen Rider Black RX.

The Sun Bask is a system on the abdomen to collect and store sunlight energy. The transformation belt Sunriser transforms power from the Kingstone and power collected by the Sun Bask into hybrid energy, which gives Black RX more power than Black. The Sun Bask also allow Black RX to recover from injury instantly under sunlight.