|This article is about a/an alternate reality/A.R. World (another rider's world) in Kamen Rider Decade.|
The World of Kabuto (カブトの世界 Kabuto no Sekai) is the alternate reality where a version of Kamen Rider Kabuto takes place. The backdrop used to enter this world depicts Tokyo Tower with an arm outstretched in homage to Souji Tendou's "walking the path to heaven" pose. Within this A.R. World, Tsukasa assumes the role of a ZECTrooper and given the ability to see in Clock Up space. Daiki's treasure in this world is the Clock Up System.
After helping the DenLiner gang in the past, Tsukasa and company began their venture in the World of Kabuto. Posing as a ZECTrooper, Tsukasa was deployed to aid Bright Troopers in the containment of a Worm as Kamen Riders Gatack and TheBee managed to exterminate it with the unseen aid of Kabuto. Soon after, Tsukasa brought Arata to the Studio to explain about his world, only to find a Worm had mimicked Tsukasa's form. After Natsumi used the pressure point to expose one of the Tsukasas as a Worm, Decade fought it before it attacked a girl and was destroyed by Kabuto. Deciding to investigate the girl Mayu, they hosted a photo shoot for her, and Natsumi learned of Mayu's older brother who was supposedly killed by Kabuto. At ZECT's headquarters, TheBee's user, Sou Otogiri, told Arata that the final prepation for the plans to capture Kabuto were nearly done. Tsukasa talked with Mayu more about her brother after attempting to help at her grandmother's oden shop, the Heaven House, and when walking back to the Hikari Studio they were attacked by a Geophilid Worm. Tsukasa destroyed it as Kuuga Pegasus Form, and was then attacked by TheBee and Gatack. After being unable to use Den-O's powers against the Riders, Decade was eventually assisted by Diend who fought Gatack to gain his Clock Up system while TheBee and Decade battled, eventually becoming Faiz in Axel Form to match TheBee's Clock Up. When Decade realized Mayu was in the same area being attacked by Worms, he gone off to save her but was intercepted by an attack from TheBee. Just as TheBee's stray shots were within inches of Mayu, Kabuto arrived to save her from both the attack and the Worms, disappearing as everyone's transformations ended. However, when Mayu saw Sou, she recognized him as her brother.
Believing that TheBee's user was her brother, Mayu attempted to look for him with Natsumi's aid until they were attacked by a Worm. Counting on Kabuto to save them, Diend fought him to acquire his Clock Up system, summoning Ixa and Psyga to hold him down before Kabuto defeated them and runs off. By the time Tsukasa found Natsumi and Mayu, the latter was shocked that she became a Worm as she ran off. She ran into Sou who revealed himself as the Phylloxera Worm and brought her to ZECT HQ as part of the Kabuto Capture plan, much to Arata's dismay before he was beaten to a bloody pulp questioning the plan. After escaping, Arata made his way to Tsukasa and revealed the plan to him, confirming Tsukasa's notion. Kabuto fell for the trap as the Clock Down took effect while the Worms revealed themselves among the ZECTroopers, with Sou exposing Kabuto as Mayu's real brother Souji. Tsukasa arrived and revealed the truth behind the Phylloxera Worm to Mayu while explaining that Souji and Mayu were still family regardless of the latter being a Worm. But believing he had the advantage, the Phylloxera Worm siced his Worm minions on Tsukasa. Souji freed Mayu and joined Tsukasa as they assumed their Rider forms to finish off the Salis Worms before forcing the Phylloxera Worm into the open. Decade and Kabuto finished him off, but the tower projecting the Clock Down waves was destroyed in the process, forcing Souji to fade back into Clock Up space with Mayu watching. After taking Mayu home and giving Daiki a "treasure" for his trouble, Tsukasa and company began the final phase of their journey, the World of Hibiki.
Souji later appears to help revive Tsukasa in Kamen Rider × Kamen Rider W & Decade: Movie War 2010 and battles Super Shocker, assuming Hyper Form as a result of Decade's K-Touch and later into his Zecter Kabuto form with the All Rider Final Form Ride Card to fight the Super Crisis Fortress.
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 Kabuto 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 Kabuto is the third and last of the three remaining worlds the Hikari Studio group, Tsukasa/Decade, Kaito/Diend, and Natsumi, explore during the novel.
Moving onto the world of Kabuto, they meet Souji Tendou, still as arrogant and confident as ever, and considers himself as the strongest Rider ever. The group enters Bistro La Salle where Hiyori Kusakabe works. Hiyori sees Kaito and Tsukasa, dressed as a ZECTroopers, 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 only a pair of chopsticks. 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. For some inexplicable reason, Tendou has the Clock Up AttackRide Rider Card and gives it to Tsukasa after he realizes that he is Kamen Rider Decade. Tsukasa uses the Clock Up card as Kuuga, meaning the AttackRide cards aren’t restricted to their respective Riders in the novel. In the end, the Worms that impersonate both Tsukasa and Kaito have been defeated. As the fight is over the trio goes back to Tsukasa’s world.
- When Tsukasa first arrived in this world, he can be seen pointing his finger to the sky in a similar way how the original and this world's Kabuto.
- The restaurant ran by Mayu's grandmother "Tendouya" is also a nod to Tendou, as well based on the Bistro La Salle, where Hiyori and Kagami are working, and Tendou being a valued customer.
- As with in the World of Faiz, many of the Rider's transformation devices (among them including the Sasword Zecter) are seen briefly.
- When one of the ZECT Riders change into their Rider Form, the Zecter didn't annouce "Change (type of insect)" and it never announce when the Rider performs their finisher (although for Kabuto, it did, but he didn't flip the horn again on the Kabuto Zecter).