Yui Haga is a Japanese manga artist, illustrator, and original character designer. Haga was born in Tokyo and raised in Chiba Prefecture. Information regarding their gender is not consistently documented across sources, with references sometimes listing them as female and others opting to not specify. Haga began working as an illustrator during university and has since built a career spanning manga serialization, light novel illustration, and adult game original art.

Haga is the author of the manga series Astarotte's Toy, originally titled Lotte no Omocha! in Japanese. The series was serialized in ASCII Media Works' Dengeki Maoh magazine, running from the August 2007 issue to the February 2014 issue. The complete work was compiled into nine tankōbon volumes. The story is a fantasy comedy centered on a young succubus princess who, despite needing to form a male harem, despises men and demands a human be brought to her world, leading to the arrival of a single father and his daughter.

The manga was adapted into an anime television series that aired in 2011. For the anime adaptation, the title was changed to Astarotte no Omocha! to avoid confusion with a corporate brand. The anime was produced by the studio Diomedéa and directed by Fumitoshi Oizaki.

Beyond this work, Haga is widely recognized as the illustrator for the popular light novel series Baka and Test, written by Kenji Inoue. The series, published under the Famitsu Bunko imprint, was a significant success and spawned multiple anime adaptations. Haga has also created another manga series titled Sakura Nadeshiko, which was serialized in Dengeki Maoh and published in three volumes between 2016 and 2018. In the field of game illustration, Haga provided original art and SD character designs for several adult games in the early 2000s, including titles for the studios Windmill and Kiss next. Additionally, Haga contributed ending illustrations for the Nisemonogatari anime series.