Kohtaro Minami

Kotaro Minami is the main character of Kamen Rider BLACK and Kamen Rider BLACK RX. He has appeared as the title character in both series. In Kamen Rider Decade there are two Kotaro Minamis that are independently BLACK and RX.

History
Kotaro was born on the day of a solar eclipse along with his stepbrother Nobuhiko Akizuki. The Gorgom noticed this, both brothers were heirs to their leader's throne. Once the two were of age, they were captured by the Gorgom and were infused with Kingstones, Kotaro was infused with the Stone of the Sun to become Century King Black Sun. However before the final brainwashing, Kotaro's legal guardian and Nobuhiko's father, Soichiro Akizuki interrupted the final stage with Kotaro barely escaping.

Soichiro reveals to Kotaro that his real parents were killed by the Gorgom when he was a baby, before he himself was killed by five of Gorgom's Spider Mutants. Kotaro transformed and after defeating the mutants took the identity Kamen Rider BLACK to fight Gorgom. As BLACK, Kotaro gains friends from Nobuhiko's family as well as a friendly Gorgom mutant. Eventually Kotaro reunites with Nobuhiko; however, Nobuhiko was converted into the perfected Century King, Shadow Moon. In their fight, BLACK was killed and his family had to evacuate from Gorgom's reign over Japan. Eventually BLACK was resurrected and fought his way through hoards of monsters until fighting Shadow Moon and presumably killing him. Using the Satan Sabre used by Shadow Moon, BLACK fought against the Creation King of Gorgom and destroys him. With the Gorgom defeated, Kotaro visits the Capitola bar before leaving for unknown parts.

Half a year after the defeat of Gorgom, Kotaro is left homeless until he is adopted into the Sahara family. He became a helicopter pilot for his new family's business due to their connections, beginning a new life for himself. Unfortunately, five years later Kotaro was abducted into the Crisis Empire mothership. The empire was aware of his identity as BLACK and gave him an offer to join them. Kotaro refused and fought back but was incapacitated with the Kingsteon damaged. He was ejected into space floating aimlessly until the sun's radiation altered his Kingsone. When his pod entered Earth's atmosphere, Kotaro miraculously survived and had gained new power. His rider form evolved into Kamen Rider BLACK RX. With his new form and power he fought against the Crisis Empire.

When his adoptive sister Hitomi is kidnapped by Maribaron to assume the identity of the Crisis Empire's only living heir, Kotaro uses Deathgaron to enter the Desert of Death after them. By the time he finds Hitomi, Kotaro falls into a trap set up by Maribaron to do away with him and Deathgaron. When it looked as if Death Gron had actually killed Hitomi, RX was in a state of sorrow and sadness over the death of Hitomi invokes a new power, RoboRider. Using his power, RoboRider fatally wounds Deathgaron before learning that the Hitomi killed was a fake and the real one is being taken to the Miraculous Valley. On his way, he meets Joe the Haze who is under the control of Nexticker, freeing him before they and Shigeru are captured by Maribaron and the Princess Karuoriya. It was after they break free that Kotaro realizes the princess is Hitomi, who was abducted to replace the real princess who died and was force grown by the nearby waterfall. When he attempts to restore Hitomi memory, Kotaro is forced to surrender when the Triplon captured Shigeru and Joe. Kotaro was then placed into a room for a hole designed to counter his abilities as both RX and RoboRider for a slow painful death. His rage to save those he loves invokes another new form, Bio Rider. After killing Triplon, with Shigeru's help, Kotaros in having Hitomi regain his memory as she and the others are return to their original ages by the people who originally resided in the valley. With only Joe and Shigeru knowing his identity, Kotaro returns to Earth.

During the middle of the series, Shadow Moon mysteriously returns to seek revenge against him, shortly after, Shadow Moon was finally defeated when RX thrusted the Revolcane through Shadow Moon's Kingstone, effectively turning him good shortly before he died and finally reverting to Nobuhiko. In the finale, he was helped by the 10 veteran Kamen Riders to destroy the Crisis Empire.

Kamen Rider Decade
In Kamen Rider Decade, a two episode arc features two different Kotaro Minamis who are independently Kamen Rider Black and RX. RX was first encountered Tsukasa Kadoya and company in the RX World when Tsukasa is dressed as Joe the Haze. After Schwarian arrives mistaking Tsukasa for Joe, RX arrived to fight. When Tsukasa becomes Decade, RX attacks him hearing of Decade's status of the Destroyer of Worlds. Natsumi tells him that Tsukasa is not a threat and agrees to work with them to fight Dai-Shocker. When Decade is transported to another world he encounters another Kotaro Minami that is Kamen Rider BLACK. Having been warned of Decade, BLACK fights him but is driven off by Kamen Rider Diend. After seeing BLACK protect a girl from Apollo Geist, BLACK decides to ally with him to fight Dai-Shocker and reveals that Joe the Haze is in his world and is helping him. Decade and Black then fight Schwarian with BLACK helping Decade get back to RX's world by using the King Stone Flash on a dimensional wall. Returning Decade and RX prepare to fight against Apollo Geist and Schwarian. Diend then summons BLACK from the card Decade receives. As Tsukasa leaves to help Natsumi, the BLACKs defeat Apollo Geist with a Double Kick. As BLACK disappears back into his world, RX meets up with Tsukasa happy that Joe is safe in BLACK's world.

At the end of the fight with Dai-Shocker in All Riders vs. Dai-Shocker, the original Kotaro Minami appears untransformed from BLACK RX.

Rider Forms
After having the Stone of the Sun implanted into him, Kotaro became Kamen Rider Black who used the power of the Kingstone to transform and charge his attacks. After being ejected into space by the Crisis Empire, Kotaro's Kingstone evolved giving him the power to use the more powerful and versatile BLACK RX form.

Trivia

 * There have been four instances where Kamen Rider BLACK and RX have existed independently from each other.
 * The first was in Kamen Rider: Run All Over the World where a timewarp causes Kotaro to meet his past self.
 * The second was in the two episode arc of Kamen Rider Decade (Series).
 * The third was in Kamen Rider Decade: All Riders vs. Dai-Shocker
 * The fourth was in OOO, Den-O, All Riders: Let's Go Kamen Riders