- Height: 171cm
- Weight: 80kg
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Ryutaros (リュウタロス, Ryūtarosu?) is the fourth Imagin that gives Ryotaro his power, which allows for the transformation into Den-O Gun Form. His natural weapon as an Imagin is a shotgun named the Ryuvolver (リュウボルバー, Ryūborubā?). Though he is the last Imagin to appear, Ryutaros initially had tried to possess Ryotaro the moment that Urataros did, and simply hid himself from the others. Ryutaros reveals himself in his form when he is attracted by Naomi's coffee inside the Den-Liner. Ryutaros is most childish in personality with a love for drawing and animals. Ryutaros also appears to enjoy break dancing, to the point to that it is incorporated into his fighting style. This recklessness also causes the most collateral damage, as he fires his gun aimlessly. When he possesses Ryotaro, he first asks "Is it okay if…?" (…いい？, …Ii??, usually "Is it okay if I beat you up?" or "Is it okay if I end it?") followed by "Your answer doesn't matter" (答えは聞いてない, Kotae wa kiitenai?). He has the ability to control people simply by snapping his fingers. This tactic works with summoning the Machine DenBird as well. Originally, Ryutaros forms a contract with Ryotaro after being promised the title of become the Den-Liner's conductor by Kai, who also gives the Imagin a ticket, on the condition that he destroys Ryotaro. However, because he does not wish for Airi to cry, Ryutaros decides not to destroy Ryotaro. The only individual he will listen to is Airi, whom he affectionately calls "sis" (お姉ちゃん, onee-chan?, Ryotaro only calls her the more formal "sister" (姉さん, nee-san?)).
Because he knows that Airi has loved Yuto Sakurai, and from faulty advice on love from Kintaros, he becomes jealous of Yuto and wishes to show that he is stronger than him. This disaster ends in Ryutaros being stopped by Ryotaro, this time with a severe warning. Ryutaros is also credited with being the one who allowed Sieg to come upon the Den-Liner, even allowing him access to a luxurious train car. During the events of Kamen Rider Den-O: I'm Born!, Ryutaros possesses the Ryotaro that Yuto brought for the Climax Scene. This has a negative side effect which caused Ryutaros to fade from existence were it not for Ryotaro's feelings condensing his remains into the K-Taros, restoring him to normal while allowing Ryutaros to form the chest armor of Den-O's Climax Form until his synch with Ryotaro was negated. However, Ryutaros drew up the concept design of the DenKamen Sword, his power now accessed in the Ryu-Gun Mode. Eventually, Ryutaros meets up with Kai, putting Ryutaros in an awkward position as he aids with sabotaging the Zero-Liner without knowing the consequences of the Den-Liner being taken and rendered powerless. Due to the event, Ryutaros matures and takes the new timeline's effects hard, being forced to give up his desire to be with Airi as she recognized him not to be her Ryotaro. After Ryotaro stands up to Kai for him, Ryutaros is now more willing to help Ryotaro out in any way he can. Ryutaros can perform his own variation of Gun Form's finisher, Wild Shot, although it is simply a powered shot due to the lack of additional charges.
As the new year approaches, Ryutaros is saddened over both Kintaros's and Urataros's decision to abandon the Den-Liner and remain in the past to fend off the Imagin army. During the final battle, he catches Ryotaro as he falls from a building at the last second, and is the first to fight the Death Imagin as Den-O Gun Form, his power for the finishing blow against the Death Imagin. During the events of "Final Countdown", Ryutaros assumes Gun Form during the epic battle against the revived Imagin. During the events of Climax Deka, as a member of the Den-Liner Police, Ryutaros causes an incident while searching for the "Evil Organization", arresting anyone who merely looked suspicious. He finally gets his closure with Airi when they meet face to face and he bashfully accepts the meal she made.
He usually refers to Urataros and Kintaros as "Turtle-chan" (カメちゃん, Kame-chan?) and "Bear-chan" (クマちゃん, Kuma-chan?) respectively, excluding Momotaros as he's not based on an animal. He is referred to by the others as "Ryuta" (リュウタ, Ryūta?). After this initial arrival on the Den-Liner, he is rarely seen without a pair of headphones over his head. Early promotional material stated that his form is based on the legend of Tatsu no Ko Tarō, or Taro the Dragon Boy. TV Asahi's website for Den-O states that his form is based on Ryotaro's mental image of dragons. One of the Imagin Anime shorts discusses Ryutaros's possible namesake.