Yūko Sanpei is a Japanese actress and voice actress from Tokyo, born on February 28, 1986. She is affiliated with the talent agency Axlone. Sanpei made her voice acting debut in the anime series UFO Baby. A significant early role was her first starring part as Renton Thurston in the 2005 series Eureka Seven.

Throughout her career, Sanpei has portrayed a wide variety of characters, frequently taking on the roles of young boys. Among her most prominent and long-running roles are Nozomi Yumehara, also known as Cure Dream, in the Yes! PreCure 5 series and its sequel, and the title character Boruto Uzumaki in Boruto: Naruto Next Generations. In 2019, she won the award for Best Actress in a Leading Role at the 13th Seiyu Awards.

Sanpei's filmography includes the specific roles mentioned. She voices the character Fuuta in the long-running series Reborn!. She is also the voice of the titular character Butt Detective, known in Japanese as Oshiri Tantei, in the anime franchise, including the films Eiga Oshiri Tantei Saraba Itoshiki Aibō (Oshiri) yo and Eiga Oshiri Tantei: Star and Moon. In the science fiction series No Guns Life, she provides the voice for the character Seven. Her roles also extend to the Gundam franchise, where she voices the character 598 in Mobile Suit Gundam: Iron-Blooded Orphans – Urðr Hunt Special Edition.

Beyond these, Sanpei has built an extensive body of work across numerous other anime television series, films, and original video animations. Some of her other notable roles include Selim Bradley/Pride in Fullmetal Alchemist: Brotherhood, Tsubasa Ozora in the 2018 Captain Tsubasa, Taichi Yagami in Digimon Adventure:, and Gil in Ascendance of a Bookworm. Her career has also included work in original net animations such as Pokémon: Twilight Wings and Star Wars: Visions.