Sai Yukino, born January 26, 1982, in Ibaraki Prefecture, Japan, is a Japanese novelist known primarily for her work in the light novel genre. She made her literary debut after her submission, originally titled The Story of Saiunkoku, won the encouragement prize and the readers' prize in the inaugural Kadokawa Beans Novel Awards in 2002. This achievement led to the publication of her first novel, The Story of Saiunkoku: Hajimari no Kaze wa Akaku, by Kadokawa Shoten in October 2003, marking the beginning of her career as a professional author.

Sai Yukino is best known as the creator of The Story of Saiunkoku, a series that became a significant commercial success. The light novel series, illustrated by Kairi Yura, was serialized in The Beans magazine and ran for 18 main volumes, with the final installment released in July 2011. In addition to the main storyline, she also wrote several volumes of side stories, which were collected and published as anthologies. The series achieved cumulative sales of over 6.5 million copies.

The popularity of the original light novels led to a substantial media franchise. A manga adaptation, also illustrated by Kairi Yura, was serialized between 2005 and 2012. The property was adapted into an anime television series produced by Madhouse, which aired in two seasons. The first 39-episode season ran from April 2006 to February 2007, and the second series, titled The Story of Saiunkoku Second Series, also consisting of 39 episodes, followed from April 2007 to March 2008. A live-action Chinese drama adaptation was released in 2023.

Following the conclusion of her signature series, Sai Yukino continued to write. Her subsequent works include the fantasy light novel series Realia, also known as The Legend of the Earth Goddess, published by Shinchosha from 2014 to 2017, as well as a stand-alone novel, End of Sky, released by Kodansha in 2019, and The Eternal Summer Left Behind, published by Tokyo Sogensha in 2020. She has also contributed short stories to various anthologies. Through her body of work, Sai Yukino has established herself as a prominent author in the light novel industry, particularly known for a single, highly successful series that spanned multiple forms of media and achieved widespread popularity.