Ryotaro Nogami is a young man with a lot of bad luck. One day, he finds a strange pass and things got stranger from a mysterious girl and a large time-traveling train to being possessed by an entity called an Imagin, beings from an alternate future whose kind are attempting to change the past. Though slightly confused about the nature of the crisis, Ryotaro, along with the aid of the hot-headed, violent Imagin, dubbed Momotaros, becomes Kamen Rider Den-O, traveling to different times on the DenLiner to battle the evil Imagin to prevent them from altering the past to affect the present and future. During his adventure, Ryotaro is joined by other Imagin who aid him as well; the lying, manipulating and womanizing Urataros, the herculean (and narcoleptic) Kintaros, and the childish yet powerful Ryutaros. He later meets the mysterious Yuto Sakurai and his bumbling Imagin partner Deneb. Yuto is not only Kamen Rider Zeronos but is the younger incarnation of Ryotaro's older sister Airi's fiancé, Sakurai, who mysteriously disappeared and is tied to the mysteries involving the Imagin and a person known as the Junction Point.