A luckless boy named Ryotaro Nogami comes across a strange train pass and becomes possessed by a powerful demon as he finds himself unexpectedly becoming the a hero known as Den-O fighting strange creatures from another time.
Ryotaro discovers more about his duty as Den-O to protect the timestream as he tries to figure a way to appease Tetsuo before the Bat Imagin can ruin the past.
Ryotaro returns to the present to confront Kai and bring an end to his mad reign of terror, even if it means an end to all Imagin, including Momotaros and his allies.
A former suitor of Airi returns in hopes of winning her heart in the absence of the missing Sakurai, leading to Sakurai's younger self and even Ryutaros to respond.
When Kai begins a multi-tier attack in order to eliminate Airi, both Ryotaro and Yuuto try to stop him, with a Imagin deciding to help in trying to make sure that the past and future is protected.
On their way back to stop Kai from killing Airi, Urataros takes over the DenLiner with several other Imagin, dumping Ryotaro at the moment where his missing memory is revealed.
With Urataros causing nothing but trouble, Ryotaro is forced to make a decision regarding whether to keep the lying Imagin around while he and Hana try to figure out the Imagin's contract holder.
As Den-O has trouble dealing with the Anthopper Imagin, Sakurai contemplates the need for the final Zeronos card and the permanent damage that will occur if finally used.
Momotaros tries to prevent Urataros from causing too much chaos with Ryotaro, while Ryotaro sparks the jealousy of a boyfriend of a girl he is forced with, leading to a drastic confrontation.
Both Ryotaro and his sister Airi work to try and improve relations between the broken couple as Den-O tries to figure out the mystery behind the Imagin's attacks.
Ryotaro and Hana pursue two Imagin attacking martial artists, one to eliminate rivals while another only to prove its own strength against other opponents.
Ryotaro tries to discover the truth regarding the karate champion possessed by the Rhino Imagin, while Hana tries to make sense of the Bear Imagin and what he really desires.
After discovering the Imagin contract holder is Kasumi's father, Ryotaro tries to discover why as Kintaros keeps trying to manage resolving the crisis in his own stubborn ways.
Ryutaros continues to cause problems to the other Imagin in holding on to Ryotaro's body, forcing them to take action in order to get their partner back.
As he remains hostage by the bathhouse owner, Ryotaro tries to figure out the mystery of his relations with his former boss while trying to prevent Ryutaros from dealing with him his own way.
Ryotaro and Hana decide to clamp down on the Imagin possessing him out of fear of Den-O's health; as Ryotaro encounters a former classmate nostalgic for the past.
Yuto Sakurai's past self appears before Ryotaro to tell him to not try to be so reckless in his pursuits again as a violent Imagin suddenly makes its move in the present.
