Reo Osanai is a Japanese voice actress who began her professional career in 2021. She is affiliated with the talent agency Osawa Office and is a graduate of Yoyogi Animation Academy, where she trained in voice acting and dance. She was born on April 23 in Aomori Prefecture, Japan.

Osanai has steadily built her career with a variety of roles in television anime, web series, and video games. Early in her career, she voiced minor characters and background roles in series such as Welcome to Demon School! Iruma-kun and Shikimori's Not Just a Cutie. She has also provided voices for younger versions of characters, including baby Mash and young Abyss in Mashle: Magic and Muscles.

In 2025, Osanai was cast in several significant upcoming productions. She portrays Aoi Kusakabe in the anime series Cultural Exchange With a Game Centre Girl, which premiered in July 2025. In addition to her voice role, she performs the opening theme song for this series, Futari no Start Button, alongside co-star Sally Amaki. She is also set to voice Diana in The Case Book of Arne, an anime adaptation of a mystery adventure game scheduled to premiere in January 2026.

Looking ahead to 2026, Osanai has been confirmed for multiple main cast roles. She will play Anastasia in the television anime From Overshadowed to Overpowered: Second Reincarnation of a Talentless Sage, which is scheduled to premiere in July 2026. Additionally, she is cast as Imari Agano in the anime project Grow Up Show: Himawari no Circus-dan, also slated for a July 2026 broadcast. Other notable roles include Roaju in Farming Life in Another World 2 and Mariruri in the web anime Yamikarasu to Mayonaka no Bōken.