- Height: 185cm
- Weight: 102kg
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Momotaros (モモタロス, Momotarosu?) is the first Imagin that gives Ryotaro his power, which allows for the Sword Form transformation. He can also sense when an Imagin is rampaging in the city, subsequently alerting Ryotaro immediately. His natural weapon as an Imagin is a sword named the Momotarosword (モモタロスォード, Momotaroswōdo?). Momotaros blames Ryotaro for his Oni-like form, though it matches his personality, best described as hot blooded, arrogant, and comedic, serving as a foil to Ryotaro's own shy and cowardly personality. In fact, Momotaros is more interested in fighting than carrying out the Imagin's goal. Unfortunately, he is constantly beaten by Hana when he gets Ryotaro into trouble. When he possesses Ryotaro, declaring the words "I've Arrived!" (俺、参上！, Ore, sanjō!?) Momotaros's own personality takes over, giving Ryotaro power, confidence, and a bit of his eagerness for a good fight. His eagerness is shown in battle, where he always declares the words, "I am, from start (to finish), at the climax!" (俺は最初から（最後まで）クライマックスだぜ！, Ore wa saisho kara (saigo made) kuraimakkusu da ze!?). Momotaros is also somewhat selfish, initially fighting alongside Ryotaro in order to ensure his own survival.
Though he unknowingly places Ryotaro in unneeded danger to suit his fancy, Momotaros eventually learns to respect him and his desire to protect others. Though he demands respect, Momotaros is usually put in his place by Hana and her powerful punches. He also does not know how to swim, has a narcotic reaction to red peppers, and seems to be afraid of dogs. While he acts hostile and demeaning to the other Tarōs, he does care about them, proven by hiding his anguish while they are slowly disappearing due to the events of the Climax Scene.
Climax Form
Momotaros is the base for Den-O's Climax Form, as he has control of the head and torso and can control the other sections that the other Tarōs usually have primary control of if need be. However, due to the newly-formed Junction Point, Momotaros's synch with Ryotaro is negated. However, his power is now accessed in the DenKamen Sword's Momo-Sword Mode. Since then, Momotaros makes it his task to train Ryotaro to fight on his own, being evasive on his reasons for it. But once Ryotaro learns the truth, both he and Momotaros have a falling out. Momotaros, enraged at Ryotaro for his decision to fight without the Tarōs, fights Den-O Plat Form to test if Ryotaro can really back up his words. After Ryotaro divulges his resolve, Momotaros apologizes to him for being evasive about the recent events and the two went on to destroy the Armadillo Imagin with the other Tarōs at their side. On his own, Momotaros can perform his style of Den-O's Extreme Slash, referred as "My Hissatsu Attack, Momotaros Version" (俺の必殺技モモタロスバージョン, Ore no hissatsu waza Momotarosu Bājon?).
End of the TV series. Continuation in the film series
Momotaros is present alongside Ryotaro for the final battle, finally receiving Ryotaro's ideal wish: to fight alongside him until the very end. He manages to survive the area being wasted while holding off Kai's Imagin army, dealing the final blow to the Death Imagin with aid of the other Tarōs, Sieg, and Zeronos adding their power into his blade through "My Hissatsu Attack, Final Version" (俺の必殺技ファイナルバージョン, Ore no hissatsu waza fainaru bājon?). Ryotaro takes his leave from the Den-Liner, Momotaros is silent on the Den-Liner as it departs, only to jump to the window at the last second to say goodbye to Ryotaro and promise to meet again as the Den-Liner departs back into the timestream. That promise is kept during the events of "Final Countdown" when Momotaros is stuned to be fighting Ryotaro while he's possessed by the Ghost Imagin, nearly getting himself killed to free his friend as they fight together against Shiro with Ryotaro's grandson aiding them. Later, he becomes a hot-blooded member of the Den-Liner Police that is formed to battle Negataros. Though Negataros was destroyed, Momotaros keeps the new group together as he sees being a cop as a cool thing.
Decade and Battleship Onigashima
When the recently de-aged Ryotaro leaves to investigate the Oni disturbance in the past, Momotaros loses his physical form and possesses Yuusuke Onodera, allowing him the ability to transform into Den-O sword form. He counters the threat of the Imagin with Tsukasa Kadoya, Kamen Rider Decade and eventually becomes his ally, as he acquires the Final Attack Ride Card 'Ore Sanjou'. After Decade's trip in the main rider continuity (Den-O's world), they all realize that time has gone awry and that even Momotaros was sent to the past in the Oni War, which the Den-O team and Decade fight in to ensure that the Oni from years past are exterminated, as history says.
Somehow, Daiki Kaitoh also has possession of Den-O Kamen Ride cards including a summon card for Momotaros.
When insulting another Imagin, he usually calls them a "X-Jerk" (Ｘ野郎, X-yarō?), while referring to Hana as literally "Nosy Woman" (ハナクソ女, Hanakuso Onna?). He usually refers to Urataros as "Turtle" (カメ, Kame?), "Turtle-Boy" (カメ子, Kame-ko?), or "Turtle-Jerk" (カメ野郎, Kame-yarō?) and Kintaros as "Bear" (クマ, Kuma?), "Bear-Boy" (クマ子, Kuma-ko?), "Bear-Jerk" (クマ野郎, Kuma-yarō?). He calls the younger Ryutaros a "Brat" (小僧、ガキ, Kozō, Gaki?) and a "Snot-nosed Brat" (ハナタレ小僧, Hanatare Kozō?). He calls Deneb "Tubby" (オデブ, Odebu?) and Sieg "Bird-Jerk". He also puts emphasis on his final blow attacks, saying "My Hissatsu Attack, Part X" (俺の必殺技パートＸ, Ore no hissatsu waza pāto X?) while possessing Ryotaro in Den-O Sword Form, with a Part 1, 2, 2’ (Two-Dash), 3, and 5 (Ryotaro tells Momotaros that he skipped 4, but he considers not using 4 "cool", even counting from 1-10 while skipping 4). In his battle against Kamen Rider Gaoh, Den-O Sword Form swiped the Rider Pass over the Den-O Belt twice, initiating a doubled Full Charge for "My Hissatsu Attack, Special Edition" (俺の必殺技・特別編, Ore no hissatsu waza tokubetsu hen?). His form is based on the legend of Momotarō, the Peach Boy, who fought the red Oni that Momotaros resembles.