After helping the DenLiner gang in the past, Tsukasa and company begin their venture in the World of Kabuto. Posing as a ZECT Trooper, Tsukasa is deployed to aid Bright Troopers in the containment of a Worm as Kamen Riders Gatack and TheBee manage to exterminate it with the unseen aid of Kabuto. Soon after, Tsukasa brings Arata to the Studio to explain about his world, only to find a Worm had mimicked Tsukasa's form. After Natsumi uses the pressure point to expose one of the Tsukasas as a Worm, Decade fights it before it attacks a girl and is destroyed by Kabuto. Deciding to investigate the girl Mayu, they host a photo shoot for her, and Natsumi learns of Mayu's older brother who was supposedly killed by Kabuto. At ZECT's headquarters, TheBee's user, Sou Otogiri, tells Arata that the final prepation for the plans to capture Kabuto are nearly done. Tsukasa talks 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 are attacked by a Geophilid Worm. Tsukasa destroys it as Kuuga Pegasus Form, and is then attacked by TheBee and Gatack. After being unable to use Den-O's powers against the Riders, Decade is eventually assisted by Diend who fights Gatack to gain his Clock Up system while TheBee and Decade battle, eventually becoming Faiz in Axel Form to match TheBee's Clock Up. When Decade realizes Mayu is in the same area being attacked by Worms, he goes off to save her but is intercepted by an attack from TheBee. Just as TheBee's stray shots are within inches of Mayu, Kabuto arrives to save her from both the attack and the Worms, disappearing as everyone's transformations end. However, when Mayu sees Sou, she recognizes him as her brother.[16]
