|Kanji Name:||歌星 賢吾|
|Romaji Name:||Utahoshi Kengo|
|First Appearance:||The Transform of Youth|
|Club:||Kamen Rider Club|
Kengo Utahoshi (歌星 賢吾, Utahoshi Kengo) is the one of the main protagonist in Kamen Rider Fourze acting as the partner for the lead protagonist, Gentaro Kisaragi. He is also the original owner of the Fourze system until he gave it to Gentaro to become Kamen Rider Fourze due to his weak health. He is however able to use the Powerdizer powered exosuit to assist Fourze in battle, but only for a limited amount of time.
He like other Amanogawa High School student (expert Gentaro), wears the school student uniform. A blue-colored jacket with a red tie, black jeans.
He is a second-year student and Gentaro's partner who is physically weak but possesses a strong will. His father was an OSTO scientist who devised the Astro Switches before the space station he worked on was destroyed. It would be by chance that Kengo finds a secret locker on the school grounds that holds a cosmic energy-based portal from to the Rabbit Hatch lunar base that remained of the OSTO complex. Though he originally intended to fight the Zodiarts on his own, his physique is so weak that even manning the Powerdizer exo-suit for extended periods is an extremely difficult task to him. He is forced to give Gentaro the means to become Kamen Rider Fourze and aid the Kamen Rider by providing him with his arsenal as well as acting as Gentaro's tactician. Kengo has not accepted becoming a member of the Kamen Rider Club, or even acknowledge the existence of the said Club. Though he is Gentaro's partner, he insists that Gentaro refers to him by his surname instead of his given name, and much to his chagrin, Gentaro refuses to do so. He eventually relents as he comes to view Gentaro as friend, instead of merely a necessary partner, calling him by his given name instead of his surname.
- He along wth Yuki Jojima has a non-speacking cameo in the end of Kamen Rider OOO.