Yu Koyanagi was the original drummer of ONE OK ROCK and a founding member of the band. Active during its early indie phase, Yu contributed to the group's first demo recordings and helped establish the foundational rhythm section that supported their pop-punk influenced sound. He is also credited with suggesting the band's name. Though he left before the band's major debut, his involvement during the band's formative years laid part of the groundwork for their future direction. After his departure in 2006, Tomoya replaced him as the band's permanent drummer.

Yu began working as a model at the age of three, encouraged by his mother. In 2005, he joined ONE OK ROCK as the drummer, contributing to the band's earliest phase before leaving in 2006 to focus on acting. He graduated from Horikoshi High School, a school known for many celebrity alumni.

He made his film debut in A Song to the Sun (タイヨウのうた) in 2006. In 2008, his performance in Tokyo Sonata earned him the Best New Actor Award at the Takasaki Film Festival. His first lead role in a film came in 2010 with Ultraman Zero THE MOVIE: Super Decisive Battle! Belial Galactic Empire.

Notable TV appearances include:

• 2009 NHK morning drama Tsubasa (連続テレビ小説「つばさ」)
• 2011 family drama Marumo no Okite (マルモのおきて)
• 2012 Taiga drama Taira no Kiyomori (平清盛)

He also made his stage debut in December 2012 with the play Ieyasu to Anjin (家康と按針).