|This article is about a/an duo of Kamen Riders in Kamen Rider Black.|
The Century Kings (世紀王 Seiki Ō) are the two candidates for the leadership of Gorgom. Every 50,000 years, the existing Creation King dies. When this time draws near, two Century Kings are chosen, eventually to fight each other, the winner claiming both Kingstones (and the loser's life, if not in the battle then in the extraction of the Kingstone.) and becoming a new Creation King, to rule Gorgom for the next 50,000 years. It is for this that Kotaro Minami and Nobuhiko Akizuki were chosen.
Kohtaro Minami (南 光太郎 Minami Kōtarō) is a 19-year-old man who became a cyborg after the Gorgom captured him and his stepbrother Nobuhiko. Using the power of the Kingstone, he shouts "Transform" and poses to become the mighty Kamen Rider Black (仮面ライダーBLACK Kamen Raidā Burakku). He is referred by Gorgom as "Black Sun". He eventually stopped Gorgom without becoming corrupted. A few years during the events of Kamen Rider Black RX, Kotaro lives with the Sahara Family and was captured by the Crisis Empire when the Skullma were sent to bring him to them. Refusing to side with the Crisis Empire, they shattered his Kingstone into two pieces, thus rendering him unable to transform into Kamen Rider Black. He was then thrown into outer space, where the sun's radiation mutated his Kingstone and allowing him to evolve into Kamen Rider Black RX (仮面ライダーBLACK RX Kamen Raidā Burakku Āru Ekkusu) to fight the Crisis Empire and the Strange Demon Soldiers.
Nobuhiko Akizuki (秋月 信彦 Akizuki Nobuhiko) is the stepbrother of Kotaro Minami who was also captured by Gorgom to became a cyborg-like his stepbrother. However, he was abandoned and was hibernated until he emerges as the Century King Shadow Moon (世紀王シャドームーン Seiki Ō Shadō Mūn) armed with his Kingstone and his Satan Saber. Unlike Kotaro who managed to escape the brainwashing, Nobuhiko was brainwashed into becoming obsessed with defeating Kotaro and taking his Kingstone to become the next Creation King. In the series finale, Shadow Moon was weakened by Kamen Rider Black using the Satan Saber to slash the Kingstone and left him inside the Gorgom Headquarters when it explodes. During the events of Black RX, He mysteriously came back to seek revenge against Minami Kotaro. He now uses the twin Shadow Sabers similar to the Satan Saber. He was finally defeated by RX when he thrust the Revolcane through his Kingstone. He then saved innocent kids and peacefully died. It`s unknown if he regained his humanity, but since is body turned back into Nobuhiko, it`s hinted that he did.