Yuto Sakurai (桜井 侑斗, Sakurai Yūto?, portrayed by Yuichi Nakamura) is a man who bears the same name as Airi's fiancé, referred in the series as the "Past Man" (過去の男, Kako no Otoko?, portrayed by Tomonobu Okano), who mysteriously disappeared prior to the beginning of the series, but similarities do not go any further it would seem. It is later revealed that Yuto is the very same Yuto Sakurai, only a decade younger, sharing his future self's high knowledge of astronomy. Prior to the series, Yuto Sakurai encounters his future self, the older Yuto Sakurai of 2007, who reveals to him the situation relating to the Imagin. Provided with the Zeronos arsenal and Deneb, Yuto takes the ZeroLiner forward in time to May 20, 2007.
Unlike Ryotaro, Yuto claims that protecting the flow of time is not the same thing as protecting people. He says that saving people is unnecessary if it means disrupting the flow of time even if it means sacrifices must be made to save the future. He holds a very spoiled personality, and often acts like a child when things do not go his way and putting lots of sugar in his coffee before actually tasting it, hence earning him the nickname "Boku-chan" (僕ちゃん?) by Urataros. Yuto is also the kind of figure who would use dishonest methods to get the job done, but has since abandoned this way of fighting. A running gag with Yuto is his hatred for shiitake, going as far as a comic beating to make sure Deneb does not serve any.
After Yuto disappears in time (during the events of Cho Kamen Rider Den-O & Decade Neo Generations: The Onigashima Warship), an even younger version of Yuto appears known only as "Yu" (ユウ, Yū?, portrayed by young actor Ruka Sawaki). Yu possesses an artifact that the Oni Brothers Goludora and Shilubara need to complete their plan. Thus Ryotaro, Kotaro and the rest of the Den-Liner crew aid him and get the artifact to the past. To protect Yu, Deneb, not knowing he is actually Yuto, asks to form a contract with him, allowing him to gain a physical form. Yu's wish for the contract is for Deneb to see his contract holder, once more. The adult Sakurai and the ZeroLiner make a cameo appearance in the end, with the former reuniting with Deneb. Yuto returns once more when his relationship with Airi begins to be threatened by the actions of the Piggies Imagin (the events of Episode Red: Zero no Star Twinkle).
When possessed by Deneb, Yuto's hair grows out past shoulder length with two locks of hair on each side of his head. On the right side, the lock is a neon green with a darker green streak within it. His personality is also overwritten by Deneb's, who is much more polite and apologizes for Yuto's actions, often by giving out Deneb Candies and acting overly friendly. This usually gets Yuto angry thus forcing Deneb out of him and comically beating him. On one occasion, he was also possessed by Urataros. Although surprised and initially annoyed, he allowed the possession to happen for a short while.
Read more about this topic: Kamen Rider Zeronos