Izumi Kasagi is a Japanese actress, voice actress, and playwright born on January 4, 1976, in Iwaki City, Fukushima Prefecture. She graduated from Japan Women's University with a degree in Cultural Studies from the Faculty of Human Social Sciences. Her interest in drama developed during her university years, where she became a regular performer in productions led by Akio Miyazawa and the Playground Regeneration Project theater company.

As a voice actress, Kasagi is best known for her role as Mamimi Samejima in the anime series FLCL. This remains one of her most recognized anime voice performances. She also provided the voice for Takana Shirakawa in the series Pyuu to Fuku Jaguar. Additionally, she voiced a parent in the film Doubutsu Sentai Zyuohger the Movie: The Heart Pounding Circus Panic.

Beyond voice acting, Kasagi has built an extensive career in live-action film and television. Her film credits include Kreutzer (2001), Summer Remix (2002), Pavilion Salamander (2006), The Last Monster (2007), Pandoras Box (2009), Golden Slumber (2010), and Residue (2016). On television, she has appeared in dramas such as Guilty: Akuma to Keiyaku Shita Onna (2010), Mother Game: Kanojo tachi no Kaikyuu (2011), Atashinchi no Danshi (2012), Amachan (2013), Doctor Investigation Team (2016), and BG: Personal Bodyguard (2018). She has also appeared in The Solitary Gourmet, Joker: Yurusarezaru sôsakan, and Namae wo nakushita onnatachi.

Kasagi is also an accomplished stage actress and playwright. In 2007, she was a finalist for Best Actress at the Yomiuri Theater Awards for her performance in Final Fantasy Super No Flat. Her script The House Key was shortlisted for the 6th Sendai Short Play Award in 2018. In 2022, her play The Sea of Moscow became a candidate for the 66th Kunio Kishida Drama Award. She won the 69th Kunio Kishida Drama Award in 2025 for her play 100 Years to the Sea. She is represented by the agency Ace Agent.