In 2011, Ōnishi had a starring role in NHK's Junior High School Diaries (中学生日記 転校生シリーズ「僕と君のメロディ」, Chūgakusei Nikki Tenkōsei Shirizu "Boku to Kimi no Melody").
In 2013 Junior High School Diaries won an International Emmy Kids Award in the series category.
[1] Ōnishi was a finalist in the 13th Japan Bishojo Contest in 2012, which led to her becoming part of an idol group called X21.
[5] Ōnishi made her debut as a voice actress later that year as Miu Ichinose in the YomeKura drama CD.
[7][8] On November 22, 2020, it was announced that Ōnishi will be making her debut as a solo singer under Nippon Columbia, with the release of her first single, "Honjitsu wa Seiten Nari" (本日は晴天なり), on March 3, 2021.