Nobuhiko Akizuki

Century King Shadow Moon (世紀王シャドームーン) is a character who serves as the primary antagonist in the Kamen Rider Series installment Kamen Rider Black. In almost all of his appearances, he is voiced by Masaki Terasoma, including the 3D short film Kamen Rider World, the 40th anniversary film OOO, Den-O, All Riders: Let's Go Kamen Riders, and the Kamen Rider/Super Sentai crossover film Kamen Rider × Super Sentai: Super Hero Taisen.

Black
Shadow Moon is the alter ego of Nobuhiko Akizuki (秋月 信彦), who had been abducted by Gorgom to become one of their new kings. Shadow Moon is both the stepbrother and rival to Kotaro Minami, who had been abducted alongside Nobuhiko but managed to escape.

Like Kamen Rider Black, Shadow Moon utilizes the King Stone to transform and is armed with the Satan Saber, a sword crafted specifically to be used by the Century Kings.

He was weakened by Kamen Rider Black using the Satan Saber to slash the Kingstone. After being defeated, Shadow Moon then harshly told Kotaro that he shall feel regret for the rest of his life knowing that he killed his best friend Nobuhiko before seemingly dying. His last known words in this series were " Black Sun.. Minami Kotaro". He was left inside the Gorgom Headquarters when his Kingstone exploded.

RX
6 months later, he mysteriously resurfaced to seek revenge against his step brother. This time, he wielded the twin Shadow Sabers, similar to the original Satan Saber, gained from the Crisis Empire. He was finally defeated by RX when he thrusts the Revolcane through Shadow Moon's Kingstone. He then admits defeat and tells Kotaro of the Crisis Empire`s plans to erupt a volcano and tells him to stop said plans while he saves the children that were being held hostage. As Kotaro then sees Nobuhiko as Shadow Moon and cries out his name, Nobuhiko claims that he is Shadow Moon who will be revived to fight Kotaro once more. He then tells Kotaro to go as he saves the kids and peacefully dies on a bed of flowers. As the children question his death, Kotaro assures them that he was resting as the kids go back to their father. Kotaro then decides that in the end, Shadow Moon truly turned back into Nobuhiko as he carries his lifeless body to presumably bury him. While it was unknown if Shadow Moon truly turned back into Nobuhiko, it was shown that his corpse turned back into human form thus hinting so.

After 0
Kotaro Minami is walking out when all of a sudden he finds himself out in the open under the moonlight and he sees someone floating around. It’s Black RX, only white. The Rider itself fights him and pulls his King Stone out and becomes the Creation King, Another Shadow Moon. The place turns into some dark temple with a throne and Shadow Moon sits down in it. Kotaro yells but Shadow Moon sneers at him and as he removes his chest armour to reveal that inside is Nobuhiko’s skeleton… and a beating heart. The fight between Black Sun and Shadow Moon was to determine which body would be most suitable for Gorgom’s ruler, the Creation King to use. He ended up in Shadow Moon’s body. And then Black turns into RX even without the King Stone and defeats Shadow Moon. Kotaro then wakes up, apparently that was all a dream.

Kamen Rider World
However, Shadow Moon would return once again as a villain in the debatedly non-canon 8-minute movie Kamen Rider World. This time, he was a giant and he was defeated by Kamen Rider J's Jumbo Formation.

OOO, Den-O, All Riders: Let's Go Kamen Riders
Due to a change in history caused by Ankh leaving a O Medal behind in 1971, Shocker achieved its goal of world dominion with the Shocker Greeed which defeated the Double Riders, and new members from the various groups that would had manifested in the normal timeline after Shocker's destruction. Shadow Moon was among the many villains who were part of this alliance. He later is defeated by Kamen Rider Decade.

Super Hero Taisen
Shadow Moon returns as a member of the revived Dai-Shocker under Tsukasa Kadoya and like all the other past villains, pretended to assist his plan to destroy the Super Sentai while working in cahoots with Dai-Zangyack to have the Kamen Riders and Super Sentai destroy each other. Once it is revealed that in fact it was Tsukasa and Captain Marvelous who were deceiving them to stop their plans, Shadow Moon joins the fight against the heroes just to be defeated along with General Jark by the combined efforts of Kamen Rider Black and the Hikari Sentai Maskman.

Super Hero Taisen Z
Shadow Moon returns again in Super Hero Taisen Z as a member of Space Shocker. He along with, Strategist Reider plot to revive Demon King Psycho to Take over the Universe. He Is Destroyed in Battle against the Kyoryugers.

Kamen Rider SD


Shadow Moon: A member of GranShocker. The brother of Black RX and apparently a Kamen Rider himself. This version of Shadow Moon tries his best to be evil, but falls short of his own expectations. He is armed with the Satan Sabre and an unknown motorcycle (possibly a Road Sector modification). He is constantly teased by Black RX, whom refers to him as "Sunshine Moon."

In other media
Shadow Moon is one of the few villains in the Kamen Rider Series to be given an action figure, Souchaku Henshin figure, and a Super Imaginive Chogokin figure. He is also one of the few Kamen Rider villains to have a Rider Kick, without being a Kamen Rider himself.

Shadow Moon was also featured as the first Secret Rare card in the Rangers Strike Masked Rider Expansion Vol. 1 and the only character in the Dark Alliance group in the Masked Rider Expansion Vol. 1.

An alternate reality version of Shadow Moon appeared in the film Kamen Rider Decade: All Riders vs. Dai-Shocker.

Personality
Before he became Shadow Moon, Nobuhiko was a kind man whom Kotaro respected and cared about. After becoming Shadow Moon, Nobuhiko became a cold, merciless man who was obsessed with defeating Kamen Rider Black and becoming the new Creation King. This was reflected by his seeming inability to revert to human form by himself. This sudden personality change would continue in RX until Kotaro seemingly finally reverts him back to normal. He then somewhat redeems himself by saving some children before dying a peaceful death. Interestingly, it was hinted in a dialogue with Kamen Rider Double in the game All Kamen Rider: Rider Generation that even as Shadow Moon, there was still something left of Nobuhiko since he tells Philip and Shotaro to warn Kotaro about Juda. This was also hinted in Black`s series as he seemed to slightly care for his sister and former girlfriend as well as hesitating to take Kotaro`s King Stone when he had the chance.

King Stone
The King Stone (キングストーン) is Shadow Moon's transformation belt. Embedded upon the center his belt is a green stone called the Stone of the Moon (月の石). Through this stone, Shadow Moon can telepathically communicate with Kotaro via his own King Stone. It was hinted in Black RX that the King Stone was somehow linked to Nobuhiko`s brainwashing as Kotaro later slashed it, thus seemingly causing Shadow Moon to regain his former personality. In theory, if Shadow Moon`s King Stone were to be broke in half then be exposed to Moonlight, He would become Shadow Moon RX.

Shadow Sabers
The Shadow Sabers (シャドーセイバー) are pairs of long and short swords manifested by the King Stone, this weapon was used as replacement for the Satan Sabre.

Battle Hopper
The Battle Hopper (バトルホッパー) is a living motorcycle created by Gorgom, made specifically for the upcoming Creation Kings Black Sun and Shadow Moon, programmed to be loyal to the strongest King Stone bearer. Battle Hopper was controlled by Shadow Moon via his Shadow Flash before Black uses his King Stone Flash to retake him from Shadow Moon. As a result, Shadow Moon attacks Battle Hopper with the Satan Sabre before Battle Hopper rams him with a suicide attack and dies.

Trivia

 * If Shadow Moon were to become a Kamen Rider, his name would presumably be "Kamen Rider Shadow" as Kamen Rider Black`s Century King name is "Black Sun" although in theory it could also be "Kamen Rider White" which would serve as a parallel to Kotaro`s Rider Form.
 * Interestingly enough, when Shadow Moon originally died, he somewhat hinted his return which eventually happened in the sequels.
 * While it was hinted in his original death that Shadow Moon turned back into Nobuhiko in the end, later sequels imply that Nobuhiko still remained as Shadow Moon since he still sides with villains and not the protagonists. It should be noted that the Shadow Moons that appeared in the sequels may have been A.R versions though.
 * Although it seemed that he still retained his memory as Nobuhiko, it was later hinted in RX`s series that had forgotten by then.