Yū Kobayashi is a Japanese voice actress and singer born on February 5, 1982, in Tokyo. She is affiliated with the talent agency Holy Peak and stands 168 cm tall. Before beginning her voice acting career, she worked as a model during her high school years. Her career as a voice actress began in 2003, and she landed her first leading role the following year as Tadamichi Aoba in the anime Dan Doh!!. Her early career was notably marked by her audition for the role of Setsuna Sakurazaki in the Negima! series, which helped establish her in the industry.

Kobayashi's voice acting portfolio is extensive, encompassing a wide range of characters across anime, video games, and film. In 2008, she was awarded the Best New Actress award at the 2nd Seiyu Awards, a recognition of her rising prominence in the field. Over the years, she has demonstrated significant versatility, frequently voicing both male and female characters. A recurring and notable role is that of Sasha Blouse in the globally popular Attack on Titan franchise, a character she has voiced across multiple seasons, films, and spin-offs such as Attack on Titan: Junior High. Another long-running role is Ayame Sarutobi, also known as Sacchan, in the long-running series Gintama. Her voice acting work also includes the role of Ruka Urushibara in Steins;Gate and Steins;Gate 0, Katsuragi in the Senran Kagura series, and Kaere Kimura in the Sayonara, Zetsubou-Sensei series.

Her career includes a diverse array of other significant roles. She served as the lead character Dan Kuso in the Bakugan Battle Brawlers franchise and voiced Konatsu in the critically acclaimed drama Descending Stories: Showa Genroku Rakugo Shinju. In the world of video games, she is known for providing the Japanese voice of Lucina in the Fire Emblem series and Enkidu in Fate/Grand Order, a role she also reprised in the Fate/Grand Order - Absolute Demonic Front: Babylonia anime adaptation. Further demonstrating her range, she has voiced characters such as Naruko Yokoshima in Seitokai Yakuindomo, Mariya Shidō in Maria Holic, Nice Holystone in Baccano!, and Chain Sumeragi in Blood Blockade Battlefront. Her more recent roles include Charlotte Roselei in Black Clover, Nami Unten in Vladlove, and Mitsuko Hiramori in Yu-Gi-Oh! Go Rush!!, among many others.

Beyond voice acting, Yū Kobayashi has pursued a career in music. She made her debut as a singer in 2007 with the single Sora no Kotoba, the ending theme for the anime Saint October, in which she also starred. In 2008, she released her first album, YOU&YU, and a mini-album, ROCK YOU!!. She later formed the musical group Crush Tears in 2010. Kobayashi is also well-known for her unique and often surreal artistic style, which has earned her the affectionate nickname Gahaku, meaning "great painter," from fans and colleagues. She announced her marriage to a non-celebrity man in December 2017.