Den-o's World
Ryotaro Nogami
Ryotaro Nogami is the original Kamen Rider Den-O and during Decade's time in his world, Ryotaro was researching the time distortions with Deneb and Kotaro, and is subsequently affected by them, causing him to regress to a younger age. While he doesn't fight in the present day, he allows the Imagin to come together and form Kamen Rider Den-O Super Climax Form in the fight on Onigashima.
Kamen Rider Den-O
Momotaros is a hot-blooded oni Imagin among the DenLiner gang who uses a sword named the Momotarosword. Due to the actions of the Oni Brothers in the past, Momotaros loses his sense of self and is unable to retain his physical form outside the DenLiner, forcing him to use Tsukasa and Yusuke as host bodies to fight the Mole Imagin as Kamen Rider Den-O Sword Form. Momotaros, while possessing Yusuke, is attacked by Diend who wishes to turn him into the DenLiner. Together with Tsukasa, Momotaros regains his true form and they destroy the Alligator Imagin, the force behind the Mole Imagin attacks whom he believed caused the crisis. But once Momotaros returns to the DenLiner and is reunited with Ryotaro and Kotaro, he learns the Oni Brothers are behind the distortions in their world, just as all he disappears, finding himself on Onigashima as part of the Oni Conquest legend. He later helps Tsukasa in Kamen Rider Decade: All Riders vs. Dai-Shocker and Kamen Rider × Kamen Rider Double & Decade: Movie War 2010. assuming his Taros form in All Riders vs. Dai-Shocker and Super Climax Form in Movie War 2010. After arriving to the World of Double, he doesn't turn into his Taros form but instead summons the DenLiner to destroy the Super Crisis Fortress.
Kohana is a little girl who lives on the DenLiner, her timeline having been erased from existence due to the Imagin going into the past. She can only exist because she is a Singularity Point, and not tied to the changes of time. She is the daughter of Yuto Sakurai and Airi Nogami, and the niece of Ryotaro Nogami.
Kotaro Nogami
Kotaro Nogami is a young man from the future who can transform into Kamen Rider New Den-O. He is the grandson of the original Kamen Rider Den-O Ryotaro Nogami.
Naomi is the waitress of the DenLiner, known for her coffee that no Imagin can resist.
The Owner of the DenLiner is a mysterious man with a habit of speaking in complexes when it comes to the nature of time. Owner enjoys eating various dishes that have a flag placed in the middle of them, aiming to eat his entire meal (usually rice or flan) without knocking the flags over.
Sieg is a swan-based Imagin with an ego who occasionally aids the DenLiner gang, providing Den-O the ability to become Wing Form. Though the crisis of the World of Den-O is seemingly solved, Sieg appears in the Hikari Studio in the World of Kabuto in the possession of a manuscript of the Onigashima Conquest legend.
One of the two Oni Brothers of Onigashima, Shilubara and his weapon is the Silvery Kanabo. He briefly appears during Den-O Ax Form's fight with Decade to acquire a vase for his brother Kuchihiko's agenda. Though ignored at the time, it would later turn out he is one of the true culprits behind the chaos in the World of Den-O.
Gelnewts are newt Mirror Monsters that serve as the Oni Brothers' foot soldiers in the Den-O World. They are armed with giant shurikens that are mounted on their backs when not in use. They accompanied Mimihiko in acquiring the vase for their masters' agenda.
The Imagin are the creatures that arrive from the future to alter the past with only a handful standing against them.Several Imagin appear in the first episode when Natsumi is trapped in shifting dimensions attempting to get her to tell them her wish. These include the Spider Imagin, Bat Imagin, Molech Imagin, Bloodsucker Imagin and Whale Imagin.
Alligator Imagin
The Alligator Imagin, based on the story of The Fox and the Crocodile, is an Imagin who enacts his own scheme to change the past. Unlike other Imagin, the Alligator Imagin goes through a multitude of hosts to enact his scheme. Arriving in the past on December 30, 2008 via a child, the Alligator Imagin proceeds to change the future and overpowers Decade and Den-O, taking the latter's DenGasher as his own. Diend and his KamenRide Card summoned Riotroopers allow for Den-O and Decade to regroup, and allow for Decade to get the Den-O Cards. With both Kuuga and Den-O, Decade destroys the Alligator Imagin with the Den-O Final Attack Ride.
New Mole Imagin
In Episodes 14-15, the Alligator Imagin's Imagin minions who appear throughout the World of Den-O. One is destroyed by Tsukasa as Den-O Sword Form. A few appear during Decade's fight with the other three forms of Den-O while Shilubara and his minions steal a vase.
Series:  Kamen Rider Decade