Rio Natsuki is a Japanese voice actress, narrator, and singer born on March 5, 1969, in Tokyo, Japan. She is affiliated with the Tokyo Actor's Consumer's Cooperative Society (Haikyō). Her vocal range is classified as mezzo-soprano. Her career began in the early 1990s, with her debut in a video game in 1993. She was previously a member of Sigma Seven before joining Haikyō in 1997.

Natsuki is known for a wide variety of roles across anime, OVA, and video game productions spanning several decades. In the long-running Tenchi Muyo! franchise, she is the voice of Rea Masaki (also known as Reia Masaki), a role she has played in various OVA releases, including Tenchi Muyo! Ryo Ohki from the third season onward, Tenchi Muyo! Ryo Ohki: Final Confrontations, and the 2016 fourth season. She is also recognized for her work in the ToHeart2 series as Lucy Maria Misora (also known as Ruko Kireinasora), appearing in the television anime and multiple OVAs such as ToHeart2 adplus, ToHeart2 adnext, and the ToHeart2 Dungeon Travelers game. Another significant recurring role is Sion Eltnam Atlasia in the Carnival Phantasm anime and the Melty Blood series of video games.

Her extensive filmography includes a diverse range of characters. In the 1990s, she voiced Miho Miho in Macross 7, Linna Yamazaki in Bubblegum Crisis Tokyo 2040, and Akari Kanzaki in the Battle Athletes series. In the early 2000s, she was cast as Miyako Inoue in Digimon Adventure 02, Hevn in GetBackers, Doris@Doll in Malice@Doll, and Rei in DT Eightron. She has also played roles such as Gretel in Yonimo Osoroshii Grimm Dōwa, Karyuu in Shadow, and Orlin Carrie in Princess Minerva. In the Super Robot Wars franchise, she voices Rio Meilong (also known as Rio Mei Long) in anime adaptations like Super Robot Wars OG: The Inspector and Super Robot Wars Original Generation - The Animation. She also voiced Akira Hōjō in Bakukyū Renpatsu!! Super B-Daman.

Beyond anime, Natsuki has an extensive body of work in video games. Some of her most prominent game roles include Lulu in Final Fantasy X and Final Fantasy X-2, Lucrecia Crescent in Dirge of Cerberus: Final Fantasy VII, and Trish Una in GioGio's Bizarre Adventure. Her involvement in long-running franchises and her ability to portray a wide spectrum of characters, from mysterious aliens like Lucy Maria Misora to motherly figures like Rea Masaki and Yui's mother in K-ON!, highlight her versatility and enduring presence in the voice acting industry.