The sibling gag comedy manga centers around Umaru, Taihei's little sister who boasts beautiful looks as well as prowess in both school and sports. However, at home she becomes a "himouto"—a slob of a girl who's only interested in games and eating.

Umaru is Taihei's little sister who boasts beautiful looks as well as prowess in both school and sports. However, she has a certain secret. She's a "Himōto" a little sister who is proper in public but lazy at home.