In public, Umaru is the perfect vision of a beautiful and smart high school girl. At home, she morphs into the ultimate slob with the ability to game all night and binge on junk food and cola. Can her big brother, Taihei, change her?

The series follows Umaru Doma, a high school girl who lives with her older brother Taihei. At school, Umaru appears to be the ideal student with good looks, top grades, and a lot of talent. Once she gets home, however, she reverts into a layabout who spends her time lying around, playing video games, and constantly depending on her older brother, much to his dismay. Over the course of the series, Umaru's alternative personalities help her become friends with her female classmates Kirie Motoba, who has a reputation of glaring at people; and Sylphynford Tachibana, a competitive school rival; both of whom turn out to be little sisters of Taihei's coworkers.