It follows Ryotaro Nogami, an unlucky young man who becomes Kamen Rider Den-O with the help of time-traveling Imagin (spirits from the future).

The show combines elements of comedy, action, and drama with a focus on time manipulation and the relationship between Ryotaro and the Imagin.

Along with the usual film adaptation that Heisei Kamen Rider series have released during the late summer of their broadcast run, Den-O had a second film released in the spring following its broadcast run which grossed 730 million yen (approximately US$6.8 million)[1] and a series of ten OVA shorts, both of which are firsts for any Kamen Rider.

Ryotaro Nogami, a young man with a lot of bad luck, 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, a 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.

To reach this goal, Imagin grant the wishes of weak-hearted humans and then go back in time to that individual's most precious memory and begin to rampage there.

A movie titled Kamen Rider Den-O & Kiva: Climax Deka (劇場版 仮面ライダー電王&キバ クライマックス刑事（デカ）, Gekijōban Kamen Raidā Den'ō Ando Kiba Kuraimakkusu Deka) appeared in theaters on April 12, 2008.

[11] The first of the films in this series is titled Cho Kamen Rider Den-O & Decade Neo Generations the Movie: The Onigashima Warship (劇場版 超・仮面ライダー電王&ディケイド NEOジェネレーションズ 鬼ヶ島の戦艦, Gekijōban Chō Kamen Raidā Den'ō Ando Dikeido Neo Jenerēshonzu Onigashima no Senkan), featuring the cast and characters of I'm Born!, Final Countdown, Kiva, and Kamen Rider Decade.

Episode Red is Kamen Rider Zeronos's chapter, and Yuichi Nakamura reprised his role for the film.

Episode Blue is Kamen Rider New Den-O's chapter, and Dori Sakurada reprised his role for the film.

Episode Yellow is Kamen Rider Diend's chapter, and Kimito Totani reprised his role for the film.

Rina Akiyama and Kenjirō Ishimaru had reprised their roles as Naomi and Owner, along with the Tarōs (Toshihiko Seki, Kōji Yusa, Masaki Terasoma and Kenichi Suzumura).

[21][22] In a later rerun of the special, Shin-chan and Nene meet up with Den-O, again, although to act as a teaser for the final episodes of Kamen Rider Den-O and to introduce Kamen Rider Kiva along with Ryotaro Nogami (Takeru Satoh) and Wataru Kurenai (Koji Seto).

The audio of Momotaros as Kamen Rider Den-O performing a finishing move is audible in the movie Jiro Dreams of Sushi.

It features a series of events involved with Hana's upcoming birthday and an evil Kamen Rider appearing with an army of Imagin at his disposal.

Taking place between episodes 44 and 45, Kamen Rider Den-O: Singing, Dancing, Great Training!!

This miniseries made more references to other Toei shows and included Ultraman Taro making a cameo appearance.

As a tie-in with Kamen Rider Kiva: King of the Castle in the Demon World, the Tarōs starred in a series of four short episodes called Momotaros's King of the Castle in Burning Red (モモタロスのまっかっか城の王, Momotarosu no Makkakka-jō no Ō), where they get into another crazy adventure as they take the Ginjiro out for a spin.

Running from December 2008 to October 2009, the story expands upon the events of Climax Deka and Kamen Rider Nega Den-O's travel through time joining forces with the Great Leader of Shocker, with Den-O and Zeronos joining forces with the original Shōwa Kamen Riders to fight them.

(仮面ライダーキバ&電王 デンライナー、宇宙へ！, Kamen Raidā Kiba Ando Den'ō Denrainā, Uchū e!)