Taking place after the events of Kamen Rider Decade episode 15, under the impression that they saved the World of Den-O, Tsukasa Kadoya and company begin their journey to the World of Kabuto when they are halted by Sieg who presents them a manuscript that detailed the legendary Oni Conquest with Momotaros' image on it. As this occurred, the Tarōs mysteriously vanish from the DenLiner as they are about to help Kotaro Nogami out with the true threat to their world.