|This article is about a/an alternate reality/A.R. World (another rider's world) in Kamen Rider Decade.|
The World of Kuuga (クウガの世界 Kūga no Sekai) is the alternate reality where a version of Kamen Rider Kuuga takes place. It was the world where Yusuke Onodera originated from before he joined Tsukasa in his journey. The backdrop used to arrive in this world shows a city with police cars and Mount Hitoki (灯溶山 Hitoki-yama) in the background. Within this A.R. World, Tsukasa assumes the guise of a police officer with the talent of understanding and speaking the Gurongi language.
The World of Kuuga was the first of the Nine Worlds the Hikari Studio traveled to, shortly after Tsukasa Kadoya became Kamen Rider Decade. Stepping outside, Tsukasa found himself in this world as a police officer while Kamen Rider Kuuga appeared to aid the police against two Gurongi.
Arriving in the World of Kuuga, Tsukasa took the guise of a policeman and watched Kuuga destroy a pair of Grongi, Ra-Dorudo-Gu and Me-Gyarido-Gi, before reverting to his human form, Yusuke Onodera. Tsukasa later destroyed Go-Baberu-Da as Decade, but was mistaken for a Gurongi by Yusuke and Ai Yashiro. When Yusuke and Ai arrived at the Hikari Studio to discuss this strange Gurongi, Tsukasa offered Ai his help in solving the mystery behind the Gurongi's female targets and the location of their lair. On the foot of Mount Hitoki, the Grongi's Lair, Tsukasa revealed he used Ai as bait to lure out the remaining Gurongi, revealing their plan to revive their leader before ruining their game. While attempting to destroy the Gurongi, Decade was attacked by Kuuga, who revealed he knew about Decade's mission and will stop him at all costs. Natsumi pleaded for them to stop, recalling her dream in which Decade and Kuuga seemingly destroyed each other. A dimensional rift occurs, and their fight is interrupted by the appearance of Kamen Riders KickHopper and PunchHopper.
After fending off the Hoppers who disappeared into another dimensional rift, Yusuke reveals he was told of Decade by a mysterious man. When Ai and her task force gone to investigate Mount Hitoki, a black mist began to rise from within, signaling the revival of N-Gamio-Zeda. Resurrected by the dimensional chaos, he used his miasma to convert humans into Gurongi. While Yusuke saved Ai and took her to the hospital, Tsukasa fought the Gurongi alone. A dying Ai requested Yusuke to overcome his angst and fight to protect everyone's smiles, and so Kuuga and Decade worked together to destroy the remaining Gurongi. N-Gamio-Zeda, in a last effort, absorbed all the Gurongi to power himself up, but he was ultimately overpowered by both Decade and Kuuga, who destroyed him with a combo attack. After returning to the hospital, Yusuke found that Ai had died and vowed to honor her dying wish, setting off on his own journey, joining the Hikari Studio with a mysterious white bat following him.
During the Rider War, though his world is destroyed, Yusuke still exists due to his traveling of the Nine Worlds. Even though he is destroyed by Decade in The Last Story, he and his world are restored, allowing him to aid in reviving Decade and defeating the newly formed Super Shocker once and for all.
- Yusuke Onodera - this world's native (and only) Kamen Rider
- Ai Yashiro - died in episode 3
- N-Gamio-Zeda - the ultimate darkness
- Gurongi - Gamio's attendants, they tried to revive him through the ultimate game
In the novel reimagination of the Kamen Rider Decade TV series, Kamen Rider Decade: The World of Tsukasa Kadoya ~The Garden Inside the Lens~, the World of Kuuga is, as one of the Nine Worlds, not an alternate reality like in the TV series but the original world. Having already traveled to six worlds, the World of Kuuga is the second of the three remaining worlds the Hikari Studio group, Tsukasa/Decade, Kaito/Diend, and Natsumi, explore during the novel.
Kuuga’s world is set somewhere early in the TV show, where Kaoru Ichijo is the only person who considers Kuuga to be an ally of humanity, while the rest of the police forces consider Kuuga as a threat. Despite having the name Yusuke Godai, his personality is actually closer to Onodera’s, if anything. Godai is an airhead for the most part, to the point of having difficulty remembering the name Decade and usually goes with “Kamen Rider Dickens.” In this world, 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, with her sentences spoken in broken grammar. This girl approaches different men saying “Do you want me?” The girl is referred as Yuri after Tsukasa sees her holding a lily flower, yuri in Japanese. She asks the question to Tsukasa, but 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 oddly suspects that Yuri is a Gurongi. This is never truly touched upon until the where Yuri reveals the truth and challenge the Riders into a fight. Her Gurongi group is not mentioned, but she’s described as a Moth, meaning she's of the Ba class of Gurongi. 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, which has traditionally been a form more focused on hand-to-hand combat. Decade's Final Form Ride for this Kuuga is also different: while it retains the ability to transform Kuuga into the Kuuga Gouram, the Gouram is described as a rhinoceros beetle, despite it traditionally being a stag beetle, which is also the same insect Kuuga is based on. Godai gives Tsukasa a thumbs up as they leave.