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) and a series of ten OVA shorts, both of which are firsts for any Kamen Rider. Continuing the trend, Kamen Rider Den-O also had a third film released in October 2008, the first for any Kamen Rider series and a second series of 12 OVA shorts was released in November 2008. Takeru Satoh claims that the reason that Den-O has amassed such popularity is because of its comedic timing. A fourth film was released on May 1, 2009, and three more released in the summer of 2010.
The catchphrases for the series are "Traveling through time, here I come!" (時を超えて 俺、参上!,Toki o koete ore, sanjō!) and "The time train, DenLiner! Will its next stop be in the past or the future?" (時の列車デンライナー!次の駅は過去か?未来か?,Toki no ressha Denrainā! Tsugi no eki wa kako ka? mirai ka?).
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.
Initially, a press release from Toei Company released on January 29, 2009, announced that there will be a fourth film for Kamen Rider Den-O. It was in production as of January 29, 2009, and was scheduled to be released in April 2009. On February 9, 2009, Toei revealed that this film was to be the first in the "Cho-Den-O" Series (「超・電王」シリーズ,"Chō-Den'ō" Shirīzu), a new multimedia franchise featuring the cast and characters of Kamen Rider Den-O and its films.
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. The first three episodes are one-minute-long, airing from July 20 to August 3 after Kamen Rider Kiva, depicting the Taros in reviewing the Go-onger and Kiva movies before Ryutaros is kidnapped by Kamen Rider Rey. The fourth two-minute-long episode showed in theaters after Kamen Rider Kiva: King of the Castle in the Demon World and Engine Sentai Go-onger: Boom Boom! Bang Bang! GekijōBang!!, with Ryutaros found by Momotaros as reenactments of the two movies by the Taros are played on the movie screen. Toshihiko Seki will reprise his role as the Imagin Momotaros and Kōji Yusa, Masaki Terasoma, and Kenichi Suzumura also reprise their roles as Urataros, Kintaros, and Ryutaros, respectively. There was a "Burning Red Ver." (まっかっかVer.,Makkakka Bā) and a "Yellow Ver." (まっきっきVer.,Makkikki Bā) of the short film, shown at specific theaters based on the announcement that Saraba Kamen Rider Den-O: Final Countdown would be playing at that theater.
"Kamen Rider Kiva & Den-O: DenLiner, Into Space!" (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!) is a planetarium show using the cast of Kiva and Den-O to teach children about the universe. It was shown at the Kagoshima Municipal Science Hall's planetarium between January 2 and March 30, 2009.