Ryutaros (リュウタロス) 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). Though he is the last Imagin to appear, Ryutaros initially possessed 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 DenLiner. 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 flashy fighting style. His personality is one of a fun-loving dancer/disc jockey and is the most dominant Den-O has. 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 possesses Ryotaro after being promised the title of become the DenLiner'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. But when Kai takes matters in his own hands in killing him, combined with realizing how he and Airi can not to be together, Ryutaros matures a bit to cope with fading away while eventually mustering courage to fight in the final battle against Kai.

He usually refers to Urataros, Kintaros, Sieg, Teddy respectively as "Turtle-chan" (カメちゃん, Kame-chan), "Bear-chan" (クマちゃん, Kuma-chan), "Bird-san" (トリさん, Tori-san), and "Blue Bear-chan" (青クマちゃん, Aoikuma-chan). However, he excludes Momotaros as he is not based on an animal and Momotaros does not understand him like the others do. He is referred to by the others as "Ryuta" (リュウタ, Ryūta?). After this initial arrival on the DenLiner, he is rarely seen without a pair of headphones over his head. One of the Tarōs, Ryutaros's basis is unclear as early promotional material stated his form to be based on the legend of Tatsu no Kotarō (Taro the Dragon Boy) while 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.