Tinker Studio

The Tinker Studio is the photography studio that the Tinker family owns and where Darren Carter develops his photographs. The various backdrops located in the studio allow it to transport its occupants to a mutltitude of parallel worlds. Its interior and exterior automatically transform to blend into the surroundings when moving across dimensions.

Darren Carter
Darren Carter is an arrogant, young man without any memory of his past. As a photographer, his photos never come out right, which is later revealed to be a sign of his world being slowly destroyed by the convergence of the other Kamen Riders' worlds. To save his world, he transforms into Kamen Rider Decade (仮面ライダーディケイド).

Summer Tinker
Summer Tinker, referred to as "Natsumikan" (夏蜜柑) by Tsukasa, is a young woman who works at the photo studio under her grandfather, having lived with him since her childhood. Prior to the series, Natsumi was a member of the Taigaku Club (退学クラブ) or TG Club (TGクラブ) for short, a group of dropouts who got bored with school and wanted to find out their own answers. But they never carry out their intent and return to school, promising to meet again years later. At the start, Natsumi begins to have nightmares of Decade prior to finding Decade's belt and giving it to Tsukasa. Fully aware of world's endangerment, Natsumi decides to accompany Tsukasa on his journey to prevent her dream from coming true.

She occasionally keeps Tsukasa in line with the Hikari Family Secret Laughing Pressure Point (光家秘伝・笑いのツボ) but she had also used the technique on other people such as Yusuke and her grandfather. She also appears to have feelings for Tsukasa, or at least cares for his well-being, which is hinted during her conversation with Yusuke Onodera. Despite Narutaki's offer to save her, she refuses and chooses to see Decade's journey to the end.

However she starts worrying during the time in the World of Hibiki after hearing from Narutaki that Decade's action is actually destroying the world. While in the World of Shinkenger, Natsumi assures Tsukasa that the Photo Studio is his home before her neardeath experience by Apollo Geist in the World of RX, learning that Tsukasa used some of his life to save her later. It is only after their adventures in the World of Amazon that Natsumi ponders if there's a point behind their journey.

In Kamen Rider Decade: The Last Story, Natsumi becomes Kamen Rider Kivala (仮面ライダーキバーラ).

Eijiro Tinker
Eijiro Hikari (光 栄次郎) is the owner of the Hikari Studio and Natsumi's grandfather. When he discovers that his photo studio is the means of accessing the A.R. Worlds by accident, he is not surprised but amused at the fact and is glad to assist Tsukasa in his mission. Whenever they arrive to a different world, he cooks a different meal each time. Eijiro is also the most easygoing of the group and gets along well with Kivala.

In the World of Decade, Eijiro is revealed to be a guise assumed by Shocker's Doctor Shinigami (死神博士), an executive member of Dai-Shocker from Switzerland. Doctor Shinigami has the ability to assume the form of the Inhumanoid Ikadevil (イカデビル), a squid monster, which he claims is his greatest creation. Though seemingly killed in the final battle by Decade, Diend, and Momotaros using several other Riders as weapons, Shinigami resumes his Eijiro guise, who seemingly forgets ever being Doctor Shinigami to begin with.

In the Kamen Rider × Kamen Rider W & Decade: Movie War 2010, the black ShinigamiHakase Memory, given to him by his longtime friend, Ryubee Sonozaki, transforms him into Super Doctor Shinigami (スーパー死神博士), though his official name is the ShinigamiHakase Dopant (死神博士・ドーパント), the leader of Super Shocker against his will due to the influence of the Gaia Memory. That is also the explanation for Eijiro becoming Shinigami in the previous movie. (In the commentary track of the Director's Cut DVD of Movie War 2010, Director Ryuta Tasaki said that Movie Wars 2010 settled the mystery of how Eijiro became Shinigami in the previous movie.) He revives the Neo Organism to defeat Kamen Rider Decade once and for all. However, Super Doctor Shinigami reverts back to Eijiro as the Memory ejects out of him caused by Kamen Rider Double HeatMetal's HardMammother Maximum Drive and he is saved by Natsumi in her Kamen Rider Kiva-la form. Afterwards he returns to the studio with the others once Ultimate D is destroyed by Decade and Double.

Yusuke Onodera
Yusuke Onodera (小野寺 ユウスケ) is a young man with a child-like personality at first who has the power to become Kamen Rider Kuuga (仮面ライダークウガ). Although originally from the World of Kuuga, he eventually joins up with the Hikari Studio group having rid his home world of the Gurongi.

Kivala
Kivala (キバーラ) is a white-colored female Kivat originally from the World of Kiva, where she is Kivat-bat the 3rd's younger sister. She is extremely tiny, small enough to be hidden in an adult's closed fist. She learns of Decade from Narutaki, and uses her power to bring Yusuke into her world, and then sends Tsukasa into another to do battle with Kaixa. She later ends up traveling with the Hikari Studio, though remaining in contact with Narutaki with only Natsumi aware of it. She seems to like Yusuke the most out of the traveling group as she is delighted when he returns to travel with them after they leave the World of Agito. In the World of Hibiki, she assists Ouja in summoning a Bakegani to be used on Decade as Gyuki was not getting the job done, placing her overall goals further into question.

In Kamen Rider × Kamen Rider W & Decade: Movie War 2010, Kiva-la is revealed to be the means for Natsumi to assume her Kamen Rider form: Kamen Rider Kivala.