Yūki Yonai is a Japanese voice actor born on December 23, 1989, in Yokote City, Akita Prefecture, Japan. He is affiliated with the talent agency 81 Produce. Before pursuing voice acting, he played baseball from elementary through junior high school and also participated in basketball and swimming. During high school, he founded an English conversation club and served as student council vice president for two years. Originally planning to attend university, he was inspired by a classmate to pursue voice acting, leading him to move to Tokyo after graduation. He attended the Tokyo Media Academy (now Tokyo Voice Acting Academy) and later the 81 Actors Studio, officially joining 81 Produce as a junior member on April 1, 2012.

Yonai began his voice acting career in 2011, with early roles including supporting parts in anime series. His first major leading role came in 2016 when he voiced Haruki Bando in the sports anime Cheer Boys!!, a role that marked a significant step in his career. The following year, he took on another lead role as Maro Kitahara in the culinary anime Piace: Watashi no Italian. He is also well-known for voicing Nazuna Nito in the multimedia franchise Ensemble Stars!, a role he has portrayed since 2015 across games, anime, and character songs. His other notable anime roles include Tokio in Shakiene!, various characters in Captain Tsubasa, and Osamu Togashi in the Destiny Child series. Beyond animation, his work extends to video games, where he has voiced characters such as the Producer in The Idolmaster Cinderella Girls U149, as well as roles in games like Atelier Lulua and Dreamia.

In the world of voice acting, Yonai has participated in several recurring collaborations, particularly within established franchises. His long-term involvement with Ensemble Stars! has included voicing the character Nazuna Nito for the game, the anime adaptation, and numerous music releases as part of the unit Ra*bits. His work in The Idolmaster Cinderella Girls U149 also represents a sustained role across different media adaptations. He has also been active in hosting web radio programs, including Cheer Boys!!: RADIO BREAKERS, related to his lead role in that series.

Regarding notable achievements, Yonai has been recognized for his versatility in portraying a wide range of characters. In 2019, he announced his marriage and the birth of his first child, sharing this personal milestone publicly. He is known for his friendly and approachable demeanor, often using the playful greeting "Ohayo-nai" on social media. His height is 159 cm, and his blood type is A. He has listed English conversation and watching DVDs among his hobbies and special skills. Regarding the specific roles mentioned in the query, he has been confirmed to voice Nazuna Nito in Ensemble Stars!, the Boy in Road to You: Kioku ni Mau Konayuki, Maro Kitahara in Piace: Watashi no Italian, and Osamu Togashi in Destiny Child.