Yuu Hayashi is a Japanese voice actor and singer born on April 2, 1983, in Zama, Kanagawa Prefecture. He began his entertainment career as a child actor in 1994, initially affiliated with the Himawari Theatre Group, where his early work included dubbing foreign dramas and films. A notable early appearance was providing the voice of a young boy in the 1995 animated film Memories. He is currently affiliated with the talent agency Ken Production.

Hayashi's voice acting career encompasses a wide range of roles in anime, video games, and dubbing. A significant turning point in his career was landing the role of the energetic and passionate Ryunosuke Tanaka in the popular sports anime Haikyu!!, a character he has voiced across multiple seasons and films, including Haikyu!! To The Top and Haikyu!! The Dumpster Battle. He gained further widespread recognition for his portrayal of the complex and influential Manjiro Mikey Sano in Tokyo Revengers. Other prominent anime roles include Olmar in Vinland Saga, Edin Dan in Tower of God, Takuya Arima in YU-NO, Michizo Tachihara in Bungo Stray Dogs, Jiro Kusano in Muhyo & Roji's Bureau of Supernatural Investigation, Yohei Kanbayashi in Paradox Live The Animation, and Takuma Ino in Jujutsu Kaisen. His film work includes Danan Rashica in Mobile Suit Gundam: Cucuruz Doan's Island.

In addition to his work in original Japanese animation, Hayashi is extensively involved in dubbing foreign content. He is the regular Japanese voice for actor Shia LaBeouf, having dubbed his performances in films such as Holes and Disturbia. He also provides the Japanese voice for Theodore in the Alvin and the Chipmunks film series and has dubbed numerous other actors and characters in projects ranging from live-action series like Smallville to animated features like The Lego Movie.

Alongside his voice acting, Hayashi is an accomplished singer. Since 2013, he has been the vocalist for the musical duo SCREEN mode, formed with composer and guitarist Masatomo Ohta and signed to the Lantis record label. The band has performed theme songs for several anime series, including Bungo Stray Dogs and the Ultraman Decker series. He also participates in multimedia projects, such as the hip-hop inspired Paradox Live, where he voices a character and contributes musically. His other interests and skills include playing the piano, strength training, and cycling, and he runs a YouTube channel where he shares music covers and personal content. Hayashi announced his marriage to a non-celebrity woman in 2024.