在与戈鲁戈姆战斗后半年，本应取回的和平突然被怪魔界克萊西斯帝国打破。克萊西斯帝国的杰克将军想拉拢南光太郎作为部下，但光太郎不答应，于是杰克将军便将其变身机能破坏。

　　变身机能破坏的情况下，光太郎被扔往宇宙。在即将变为宇宙尘埃的时候，光太郎被神秘的太阳光线照射，其体内的帝王石亦产生了变化，光太郎也因此变成了新生的光之王子·“太阳之子”假面骑士BLACK RX，并展开了与克萊西斯帝国的战斗。

Following the fall of Gorgom, Kotaro Minami tries to live a normal life with the Sahara family. However, this brief moment of peace is soon shattered by the arrival of the Crisis Empire—an evil alien menace that aims to eradicate humanity and claim dominion over Earth. After refusing to aid them in their nefarious goals, Kotaro is thrown hurtling back towards the planet with his transformation belt shattered. However, when he awakens, Kotaro discovers that the sun’s rays have blessed him with new power—the power of Kamen Rider Black RX!

ゴルゴム壊滅後、平和な生活を送っていた南光太郎に、新たな敵「クライシス帝国」の魔の手が迫る。

変身能力を奪われ宇宙空間に投げ出された光太郎であったが、体内のキングストーンに太陽の光＝宇宙の生命のエネルギーを受けて「仮面ライダーBLACK RX」へと進化。

光の必殺武器「リボルケイン」を手に、クライシス帝国への反攻を開始した！

Issamu Minami começa uma vida nova como piloto. Eram dias felizes, mas o Império Crisis aparece na Terra, anunciando uma invasão cujo objetivo é eliminar toda a humanidade. Eles capturam Issamu e tentam obrigá-lo a se aliar a Crisis, mas falham. Derrotado e jogado no espaço, a energia da King Stone é alterada devido à exposição solar, dando origem a Black RX, o Filho do Sol.