Kokage Kuga is a supporting character in Sketchbook ~full color's~. She is a short girl with dark hair that she typically wears in a ponytail, and she stands at 140 centimeters tall. She is in class 2-10, shares a December 19 birthday, and has blood type A. Her face rarely shows emotion, and her behavior often seems peculiar, which initially gives an impression of being gloomy or even sinister. However, this is misleading: she is in fact playful, mischievous, and given to joking, with an occasional morbid streak. The author of the original manga has indicated that her eccentricity is a deliberate affectation she adopts to make it easier for her to communicate with others.

Kuga is a member of her school's art club, where she interacts with the other club members such as Sora Kajiwara, Natsumi Asou, and Hazuki Torikai. In the manga, she and Natsumi sometimes ride the train together, suggesting a friendship that extends beyond club activities. She likes sea urchins and salmon, and she dislikes high places and supernatural phenomena. Her abilities as an artist are not highlighted in detail, but her presence in the art club implies a baseline talent for sketching and painting. Throughout the series, her character does not undergo dramatic development; she remains a consistently quirky and introverted presence who contributes to the group's dynamic through her dry humor and unconventional outlook.