As such, Ryotaro is drafted by the Owner of the DenLiner to become a keeper of space-time. Kamen Rider Den-O destroys Imagin that travel to the past to change the future, enabling that the future of the humans remains in tact. Along the way, Ryotaro becomes contracted to the Imagin Urataros, Kintaros, and Ryutaros (together they are known as the Taros), enabling Den-O to transform into additional forms. Ryotaro also discovers the existence of Yuto Sakurai, the younger incarnation of his sister's fiance, who become Zeronos. The group also help the Imagin Sieg who nearly ceases to exist, and later use his partnership with Ryotaro to fight the evil Kamen Rider Gaoh when the Edo period is threatened. It is also in this travel back in time that Ryotaro meets his younger self dubbed "Kotaro" who becomes Kamen Rider Mini Den-O to help with the fight. When three of the Taros' existence is threatened by their part in defeating Gaoh, Ryotaro's feelings for them creates the K-Taros cellphone, bringing them back to life and allowing him to become Climax Form. When Kai, the Singularity Point of the Imagin's future, appears to further his plan to destroy the Junction Point to ensure that the flow of time ensures that the Imagin will exist rather than humans, Ryotaro's sync with the Taros begins to fade, forcing him to fight on his own as Liner Form.
Ryotaro, the Taros, Yuto, and Deneb work together to save Hana and defeat Kai, ensuring that the Imagin will never exist. As Ryotaro begin to lament that he will never see the Taros again, they (along with Sieg and Deneb) make themselves known, having been saved due to their time with the Kamen Riders. The Owner tells Ryotaro that his work is done, and Ryotaro gladly relinquishes the Rider Pass, knowing that he will meet the Taros in the future. Some time after this, Ryotaro is asked by the Owner to help in finding other Imagin who survived Kai's defeat and disappearance from history. It is during this time Ryotaro comes across both the evil Negataros and the half-Fangire Wataru Kurenai. After Negataros is defeated, Ryotaro is abducted by Shiro. When the Taros and his grandson from the future Kotaro save him, he becomes Den-O once more to defeat Shiro and save all space-time from being reversed such that everyone alive becomes dead and all those who have died come back to life, as well as ensuring that his ancestors in this time period meet. Later, Ryotaro becomes de-aged in a similar way to his niece Hana, and must assist his grandson and Tsukasa Kadoya save space-time from the Oni Brothers Goludora and Shilubara. While still in his younger incarnation, Ryotaro also helps Yuto save Airi from the Piggies Imagin, help Kotaro and a young woman deal with her contract with the Mantis Imagin, and inadvertently assist Daiki Kaito steal an item from history and escape from the Time Police.