Kei Toume is a Japanese manga artist born on April 13, 1970, in Zama, Kanagawa Prefecture, Japan. She studied at Tama Art University in Tokyo, where she was a classmate of fellow manga creators Hiroaki Samura, Benkyo Tamaoki, and Hajime Ueda. Toume began her professional career in 1992 with the publication of her first manga, Rokujō gekijō, in Comic Burger magazine. The following year, this work earned her the Shiki prize in a contest held by Kodansha, and in 1994, her manga Mannequin also won a prize from the same publisher.

Toume is recognized internationally for creating the manga series Sing "Yesterday" for Me. The series was serialized in Shueisha's seinen manga magazine Business Jump from 1997 to 2011, and after that publication ceased, it moved to Grand Jump, where it ran from 2011 until its completion in 2015. The complete manga was collected in eleven tankōbon volumes. The story follows Rikuo Uozumi, a college graduate working aimlessly at a convenience store, as he navigates relationships with the eccentric Haru Nonaka and his old college friend Shinako Morinome. An anime television series adaptation produced by Doga Kobo aired from April to June 2020, consisting of twelve episodes.

Beyond Sing "Yesterday" for Me, Toume has created numerous other notable manga works. She started the series Lament of the Lamb in Comic Burger in 1996, and after that magazine ceased publication, the series continued in Comic Birz. Lament of the Lamb ran for six years and was adapted into a radio play, an anime, and a live-action film. Her other major works include Kurogane, which was serialized from 1996 to 2003 and collected in five volumes, as well as Acony, Zero, Luno, The Hour of the Mice, Our Rhythm Change, Static Noise Princess, and Gen'ei Hakurankai. Several of her manga have been translated into English, including Kurogane by Del Rey Manga and Lament of the Lamb by Tokyopop.

In addition to her manga career, Toume has contributed her artistic talents to other media. She worked as a character designer for the video games Giga Wing and Giga Wing 2, and served as a concept designer for the 2000 live-action film Sakuya yōkai den. She has also produced illustration collections, including YESTERDAYS: Sing "Yesterday" for Me Art Collection published in 2008. Her artistic style and thematic focus on melancholic atmospheres, young adult uncertainty, and the weight of past relationships have established her as a distinctive voice in seinen manga. As of 2022, she continues to create manga with the series The Old Book Life of the Momokita Family, serialized in Grand Jump.