Kamen Rider Decade’s novel is written by the new author, Aki Kanehiro. According to Shinichiro Shirakura, Aki Kanehiro is not a penname and this is actually Aki’s debut work.
The novel itself is 248 pages long, with 8 chapters and is a parallel universe. It does not follow what happened in the TV series. Throughout the novel, Tsukasa Kadoya, Natsumi Hikari and Daiki Kaito travel to 3 different worlds while stopping at Tsukasa’s world in between every world.
The group has already to 6 different worlds when the novel begins, leaving only Den-O, Kuuga and Kabuto’s world unexplored. The worlds he travels to are supposed to be the original worlds.
Tsukasa is generally the same personality wise. His world is different from the world in All Rider VS Great Shocker. He has no sister and his parents live overseas. In the novel he’s described as a young NEET tired of his mundane life, the only thing he finds interesting is photography. He ends up stumbling upon an abandoned photo studio, inside he finds an old camera standing on a tripod. Tsukasa picks it up and peeks through the viewfinder. Through the viewfinder, Tsukasa sees a completely different world. Instead of a flimsy Eijiro that knocks down a backdrop, the group uses the camera to travel between worlds. In fact, Eijiro doesn’t even exist in the novel.
The photo studio isn’t some ordinary photo studio that was just abandoned. It actually manifests itself in front of people that are tired of their own world and want to find a new world. Natsumi, Kaito and Narutaki, all found the photo studio in their own respective home worlds. There’s also no greater enemy organization, like Great Shocker.
Natsumi and Kaito are very different from their TV counterparts. Natsumi is really just the token female character, not much personality to speak about. She does practically nothing until the end, where she’s just a cheap plot device. There’s also a Natsumi from Tsukasa’s world, although she committed suicide due to worldly troubles.
Kaito is given a tragic past and is a very confused and troubled man. His entire family is brutally murdered in front of him. Out of desperation Kaito begs on his knees, hoping he’ll be spared, even going as far as to lick the murderer’s shoes. He eventually gets tired of his world and seeks to find a new one, along the way he finds the DienDriver and ends up working for Narutaki. There’s no real explanation for any of this. His homo lust for Tsukasa is carried over to the book, he insists on sharing rooms with Tsukasa shortly after Den-O’s world. Here, he has no interest for treasures.
This is however dropped after Kabuto’s world. It’s not outright said, but it’s heavily hinted that he likes Tendou. He even says he feels nauseous over how Tendou’s narcissism completes him.
Tsukasa met Natsumi in the first unnamed world he traveled to. A world where monsters are attacking humans. Natsumi sees and calls Tsukasa by the name ‘Decade’ and gives him the DecaDriver, telling him he must transform. A confused Tsukasa goes along with it and becomes Decade for the first time. They travel to another world together and meet Daiki Kaito. He acts hostile towards Tsukasa, but still decides to follow the two on their travels.
Narutaki appears here and there, yelling at Tsukasa, calling him the Destroyer of All Worlds and he’s really mad at him.
The novel doesn’t reveal much regarding the other 6 worlds they’ve already traveled and jumps straight ahead to Den-O’s world. Tsukasa’s clothes changes into a doctor’s uniform as they arrive. Tsukasa meets Ryotaro Nogami, but his Imagin friends are missing. Tsukasa agrees to help him find them. The Den-O characters feel very off-character. Momotaros comes off as rather polite compared to his TV counterpart, and actually refers people to their real names. As opposed to a snarky nickname. This world doesn’t serve much purpose other than filling out the book. The FFR is the same, Tsukasa turns Den-O into Momotaros.
Kuuga’s world is set somewhere early in the TV show, Ichijo is the only one who considers Kuuga to be an ally of humanity. While the rest of the police force consider Kuuga as a danger. Despite having the name Yusuke Godai, his personality is closer to Onodera’s. Godai is an airhead for the most part, he has trouble remembering the name Decade and usually goes with “Kamen Rider Dickens.â€
Tsukasa is dressed as a painter in Kuuga’s world.
Despite being Kuuga’s world, Tsukasa doesn’t interact much with Godai. Instead he meets a mysterious unnamed girl, her sentences written with poor grammar. This girl approaches different men saying “Do you want me?†The girl is referred as Yuri after Tsukasa sees her with a lily flower, yuri in Japanese.
She asks the question to Tsukasa, Natsumi doesn’t like it and uses her Laughing Pressure Point technique. Yuri takes a liking to Tsukasa and connects with him. Tsukasa says they are the same type of people, and relate to each other. But he reveals that he never really paid attention to her and never cared about her.
From the start, Natsumi suspects that Yuri is a Grongi. This is never touched upon until the where Yuri goes “yeah, I’m Grongi, let’s fight.†Her Grongi classification is not mentioned, but she’s described as a Moth. She causes people to explode by sticking moth scales from her wings on people. Decade and Kuuga defeat her together. Godai only uses Mighty and Dragon, but for some reason he’s using a sword while in Mighty form. Decade Final Form Rides Kuuga into Gouram, which is described as a rhinoceros beetle. Despite being a stag beetle. Godai gives Tsukasa a thumbs up as they leave.
They shortly move onto the world of Kabuto, where they meet Souji Tendou. The character description of Tendou is more or less Hiro Mizushima. Still as arrogant and confidence as ever, also the strongest Rider ever according to the novel. The group enters Bistro La Salle where Hiyori works. Hiyori sees Kaito and Tsukasa, dressed as a ZECT Trooper, claiming that the two of them ate without paying. Tendou hears this and is enraged. The three of them fight and Tendou actually beats them with a pair of chopsticks only. Turns out it was a pair of Worms that ate without paying. Tsukasa and Kaito are eventually captured by ZECT, only to have Tendou save them. Tsukasa thanks him and says that he never thanks people. Tsukasa starts respecting Tendou.
The entire chapter is about how great Souji Tendou is, that he is the absolute best. At this point, it’s not even about Decade. For some reason Tendou has a Clock Up card and gives it to Tsukasa. Tsukasa uses the Clock Up card as Kuuga, meaning the Attack Ride cards aren’t restricted to their respective Riders. They find and beat up the Tsukasa and Kaito Worms. As the fight is over the group goes back to Tsukasa’s world.
Between all the traveling, a vampire has been attacking in Tsukasa’s world. Leaving behind dried up corpses. The group investigates and they find  out that Narutaki is the vampire. Just like the group, Narutaki originally had his own homeworld, but abandoned it to find a new one. He’s been traveling for so long that his mind has been deteriorating and can barely remember who he really is. He was originally a human, but just became a vampire monster. No explanation. The Kamen Riders have a very pure energy that Narutaki seeks to consume. Narutaki threw a hissy fit because Decade has the Rider Cards, which is concentrated energy. Thus, he sends Kaito to steal them for him. Kaito gives him the 9 Heisei Rider Cards and Narutaki reveals his real form. A red demon. lolMomotaros
Kaito suddenly has a change of heart, and sacrifices himself to save Tsukasa. All hope seems to be lost, Tsukasa even uses a Diend card with the DecaDriver. Which turns him into a cyan Decade. It doesn’t do much. Narutaki beats Tsukasa so hard, he reverts into human form again. Natsumi, who had special powers all along, creates a special card with the 9 Riders on it. Tsukasa uses it, which summons the Riders to do their finishers. They then turn into cards, attaching them on Tsukasa, turning him into Final Kamen Ride Tsukasa. Basically, Complete Form without a K-Touch. Narutaki is hit by a Rider Kick.
Narutaki wanted to destroy all worlds and then create his own ideal world, he dies looking and Natsumi. Knowing that she had the power to do what he wished for.
With the crisis over, Tsukasa returns to his world and Natsumi decides to go with him and live in his world. When they return Tsukasa finds an article where it says Natsumi is dead.
A few decades later, an unchanged young Kaito appears in front of an elderly Tsukasa. Kaito tells him it’s time to visit Natsumi’s world. There they are greeted by a young Natsumi, and Tsukasa finds himself as a young man again.
