Kamen Rider Decade (仮面ライダーディケイド, Kamen Raidā Dikeido?, Masked Rider DCD, Masked Rider Decade) is the title of the first of the 2009 editions of the long-running Kamen Rider Series of tokusatsu dramas. Decade, as its title suggests, is the tenth of the Heisei Rider Series, having begun with Kamen Rider Kuuga in 2000. It began broadcast the week following the finale of Kamen Rider Kiva and is featured in Super Hero Time alongside the 2009 edition of the Super Sentai Series, Samurai Sentai Shinkenger. The series ties in with the arcade game Kamen Rider Battle: Ganbaride, with Kamen Riders Decade and Diend using cards resembling those used in the game to transform and access various weapons. The catchphrase for the series is "Destroy everything, connect everything." (å…¨ã¦ã‚’ç ´å£Šã—ã€å…¨ã¦ã‚’ç¹‹ã’, Subete o hakaishi, subete o tsunage?).

Suh-hee is left by her mother at an orphanage as a small child. She grows up at the orphanage and becomes close to Sae-joon, the son of the orphanage's director. The Director objects to her son dating Suh-hee and kicks Suh-hee out of the orphanage shortly before she graduates from high school. Suh-hee must survive on her own in the outside world. Sae-joon continues to love Suh-hee despite his mother's objections.

Bo Ye is a reluctant big star who entered the entertainment industry to support his family. Now that he has earned enough money and his contract about to end, he happily starts planning for the next stage of his life. Around the same time, unfortunate financial downturn struck his agent, his sister and his best friend. Feeling obligated to help them he contemplates on renewing his contract. Totally depressed by this thought, he buys a lotto ticket hoping that he can win the big one and save him from this dilemma. As luck would have it, he wins the jackpot but loses the ticket before he can cash it. Now he is chasing after a taxi driver, De Xing, all over town in order to get it back.

Nurhaci was an important Manchu chieftain who rose to prominence in the late 16th Century in what is today Northeastern China. He was part of the Aisin Gioro clan, and reigned from 1616 to his death in September 1626. reorganized and united various Manchu tribes, consolidated the Eight Banners military system, and eventually launched an assault on China proper´s Ming Dynasty and Korea´s Joseon Dynasty. His conquest of China´s northeastern Liaoning Province laid the groundwork for the conquest of the rest of China by his descendants, who would go on to found the Qing Dynasty in 1644.

The story's main character Mariko is a woman studying child welfare in Hokkaido. She grew up always doubtful about the love from her mother, who looked nothing like her and who passed away 9 nine years ago. One day, she finds some of her mother's belongings at a relative's house, and she heads to Tokyo to seek out the truth behind her birth. Meanwhile, Futaba is a college student living in Tokyo who is focused on her band. She gets an opportunity to appear on television, though her mother is strongly opposed to it. Naturally, Mariko is shocked when she happens to see Futaba on television, since the two of them look completely alike. ~ Tokyograph

The Kaishinmaru is a hospital ship which goes around to islands without hospitals in the Seto Inland Sea to provide medical services. The doctors and staff live communally on this ship which has facilities like a hospital as it circles theislands. One day, a lone doctor is supposed to come to the Kashinmaru. His name is Sezaki Kota. He is a young freelance general physician who hails from Hokkaido. The nurses Togami Mako and Misaki Noboru; physician Uchimura Aoi; clerical officer Hiuchi Akira who is also Aoi’s husband; ship’s captain and chef Kaito Takeshi; and the rest of the staff prepare Kota’s welcome party. However, Kota arrives much later than the appointed time. He comes across Mako who has just taken a bath and is mistaken for a prowler. She sends him a flying kick. The next day, Kota re-introduces himself to the staff and immediately gets to work. This time, the Kaishinmaru visits Chitosejima. In the morning, Kota examines the island’s residents that have gathered. However, Mako is half-outraged by Kota’s irresponsible attitude such as a recommendation to a patient who cannot get relief from a stomachache to drink carbonated drinks. In the afternoon, Kota goes out with Mako for house calls. It appears that there will be a festival on the island tomorrow and they see a man practising on drums. On the way back from the house calls, Kota notices a woman, Murakami Mizuki, crying in front of a tombstone and he is captivated by her beauty. Mizuki is the daughter of Michinori who runs a shipbuilding business on this island. She and her father are at odds. Learning that Mizuki wants to protect the house filled with memories of her late mother and opposes her father’s intention to discontinue the business and sell the house, Kota decides that he will marry her and be Michinori’s successor. And so, he announces out of the blue to the Kaishinmaru staff that he is getting off the ship tomorrow … … Kota has a terrible weakness when it comes to beautiful women. He would fall in love with a woman he meets on each island he visits, declare that he is going to live with her and make every effort to solve the problem she has. However, various people would get drawn into this fuss. In the end, he would be dumped by the woman. Then, he would tearfully go on to the next island and fall in love with another woman and the same thing would happen over and over again … …

Project Thouser is a 2-part special miniseries for Kamen Rider Zero-One. It focuses on the characters Naki and Gai Amatsu, as well as the origins of Kamen Rider Thouser.