- Ryotaro pursues the Molech Imagin to May 8, 2000 and becomes Kamen Rider Den-O to destroy the Imagin. Though it seemed the danger passed, it turned out that the Molech Imagin was under the employ of a rogue Kamen Rider named Gaoh who hijacks the DenLiner with his band of Imagin. After knocking Ryotaro out when he and Hana attempted to board the DenLiner while trapping all the Taros sae Ryutaros, Gaoh steals Owner's Master Pass with the intent to travel back in time via "God's Line" to Japan's Edo Period to retrieve the legendary God's Train, the GaohLiner. Trapped in 2000, with Ryotaro having lost all memory of Den-O, he and Hana encounter Ryotaro's younger self, later called Kotaro by the group, and the Imagin Sieg that they aided earlier. Momotaros arrives after escaping the DenLiner, but he is only able to possess Kotaro while Sieg's special talents allow him to still possess Ryotaro. Yuto shows up, taking everyone on the ZeroLiner to pursue Gaoh, with Kotaro joining them. Gaoh uses the DenLiner to damage the ZeroLiner before transforming into his Kamen Rider Form to send the gang into the Mesozoic Era before they are able to reach the Edo Period. While Yuto fixes the ZeroLiner, Ryotaro and Kyotaro talk, revealing that the event Ryotaro most regrets is losing the only remaining photograph of his parents, who died when he was young, because he cannot remember their faces without the photograph.
The next day, getting the aid of Senhime, Ryotaro and company sneak into the camp of Yukimura Sanada, who is aiding Gaoh. Though the reunited Tarōs defeat Sanada's ninjas, with Sieg destroying the Cobra Imagin as Den-O Wing Form, Gaoh succeeds in obtaining the GaohLiner and travels forward to December 26, 1988, the day Ryotaro was born, to erase that day and thus eliminate Ryotaro. After regaining his memory and his ability to transform, Ryotaro is forced to fight Gaoh along with Momotaros and his band until Yuto arrives with the past Ryotaros he borrowed for the "Climax Scene". After the long battle, the Den-Os and Zeronos emerge victorious as Gaoh's followers are wiped out and the GaohLiner is destroyed by the DenLiner and ZeroLiner. Surviving the GaohLiner's destruction, Gaoh dies in a final duel with Den-O Sword Form, reduced to sand. On the return trip to his own time, the DenLiner comes across Ryotaro's old house, allowing Ryotaro and Kotaro to see the faces of their parents. Sieg and Kotaro also return to their respective timelines as well, resuming their places in history. When Ryotaro returns to the present, he finds a drawing of his parents in the picture frame where the original photo once was.