Yui Ninomiya is a Japanese voice actress and singer born on September 6, 2001, in Kanagawa Prefecture. She is affiliated with the talent agency Horipro International and the record label Lantis.

Ninomiya began her career after winning a special award at the "Next Generation Voice Actor Miracle Audition" in 2017. She made her voice acting debut in 2018 with a leading role as Ema Hinata in the long-running anime series Aikatsu Friends!. This role marked a significant start to her career and connected her to the Aikatsu! franchise, where she later voiced Pop Melon Crepe in Aikatsu Planet! and its film adaptation.

Her filmography includes a variety of roles across different series. She voiced Luvelia Sanctos in the anime Peter Grill and the Philosopher's Time and reprised the role for its second season, Peter Grill and the Philosopher's Time Super Extra. She also played Satoru in Kaoru no Taisetsu na Mono and Rui in Mitchiri Wanko! Anima~tion. In film, she has taken on roles such as Erina Eririn Isayama in Idol Bu Show and Silvia in Guardy Girls.

In addition to voice acting, Ninomiya is also a singer. She made her solo singer debut in January 2020 under the name Ninomiya Yui with the single Ai toka Kanjō on the Lantis label. She has performed theme songs for several anime series. Notably, she performed the opening theme Tsuranuite Yūtsu for Peter Grill and the Philosopher's Time as her character Luvelia Sanctos, the ending theme for the third season of Classroom of the Elite, and the opening theme Dark Seeks Light for the series The World's Finest Assassin Gets Reincarnated in Another World as an Aristocrat. She was also part of the musical unit BEST FRIENDS! formed from the Aikatsu Friends! series.

In February 2024, Ninomiya went on a hiatus from work to focus on recovering from health issues. She announced her gradual return to work at the end of August 2024. Following her return, it was announced in September 2024 that she had left her agency, Horipro, to pursue freelance opportunities.