When the Hikari Studio appears in the World of Den-O, Tsukasa finds himself dressed in a strange detective-like attire with possession of a Rider Pass. He is then suddenly possessed by an Imagin, who battles a Mole Imagin as Kamen Rider Den-O. After taking out the Imagin, the possessed Tsukasa walks off until Natsumi uses her pressure point move to drive the Imagin out of him. When the Imagin known as Momotaros tries to possess Tsukasa, again, he throws Yusuke in front of him and Yusuke becomes possessed. After easily overcoming M-Yusuke and treating him to pudding for answers, Tsukasa learns that the Imagin lost his physical form some time before they arrived. The possessed Yusuke then runs out of the Hikari Studio to go after the other Mole Imagin with Tsukasa and Natsumi close behind as they look for the DenLiner to solve the mystery. However, Urataros, Kintaros, and Ryutaros possess Tsukasa and chase after Natsumi for answers. When Tsukasa forces the three out and they enter Natsumi to fight him, Decade uses Agito's power on each form while a mysterious Kamen Rider-like figure and his lackies attack a group of delivery men, with the Alligator Imagin taking advantage of the chaos. When a dimensional rift sends Decade and Den-O into the dimension where Natsumi saw the Rider War, the two Kamen Riders reach a stalemate as they are picked up by the DenLiner. While the DenLiner's Owner realizes that they have to work together, Yusuke and Momotaros as Den-O are in a losing battle against Diend with Narutaki as witness.[14]
