Aguri Ōnishi is a Japanese actress, voice actress, and singer born on May 2, 1997, in Aichi Prefecture, Japan. Her entertainment career began in 2011 with a starring role in the NHK educational drama segment Junior High School Diaries. In 2012, she was a finalist in the 13th Japan Bishojo Contest, which led to her becoming a founding member of the idol group X21 in January 2013. She remained with the group until her graduation in April 2017.

After leaving X21, Ōnishi shifted her focus to voice acting. She completed the Pro-Fit Voice Actor Training Course and joined the agency Link Plan Inc. in July 2017. Her voice acting debut came later that year when she voiced Miu Ichinose in a drama CD for the series YomeKura. Her early anime roles included minor characters in series such as Ms. Koizumi Loves Ramen Noodles and Tada Never Falls in Love in 2018.

Ōnishi's breakthrough role came with the Love Live! franchise. In September 2017, she was announced as the voice of Ayumu Uehara, a main character in the multimedia project that would become Love Live! Nijigasaki High School Idol Club. She has since reprised this role across numerous projects, including the mobile game Love Live! School Idol Festival ALL STARS, the two seasons of the anime television series, the theatrical OVA Love Live! Nijigasaki High School Idol Club Next Sky, the spin-off shorts Nijiyon Animation and its second season, and the concluding film trilogy. Her portrayal of Ayumu Uehara is considered her most prominent and career-defining work.

Beyond the Love Live! franchise, Ōnishi has voiced a variety of other characters. In 2019, she played Rena in the anime series Afterlost. The following year, she took on the main role of Fubuki Kitakaze in the original anime Maesetsu! Opening Act. In 2022, she voiced the titular healer, Karla, in the fantasy comedy Don't Hurt Me, My Healer!. Her other anime roles include Beth in Black Summoner, Masato Sendō in Seirei Gensouki: Spirit Chronicles, and Merielle in Loner Life in Another World. She has also contributed her voice to video games, such as Ashley in Ys X: Nordics and Sunao Toki in Magia Record.

Ōnishi has also been active as a singer. She was a member of the voice actress unit Prima Porta from 2019 until November 2020. In November 2020, it was announced that she would make her debut as a solo artist under Nippon Columbia. Her first solo single, Honjitsu wa Seiten Nari, was released on March 3, 2021. Her subsequent single, Elder Flower, was used as an ending theme song for the anime Seirei Gensouki. Her work as a solo singer earned her the Newcomer Award at the Reiwa 3rd Anison Taisho awards. Additionally, as a member of the Nijigasaki High School Idol Club group, she was part of the ensemble that won the Singing Award at the 17th Seiyu Awards in 2023.