The manga follows Rumi Ikuno, a second-year transfer student at Hanagaoka Private Girls' Academy, who despite her naivety, has a knack for causing chaos and confusion wherever she goes. Through amusing incidents, the story delves into the unusual and exasperating life of this peculiar girl.
Volume 4 includes a one-shot titled "Rumi-chan Zenya," which serves as a prototype story for "Rumi-chan ga, Ima no Rumi-chan ni Naru Sukoshi Mae no Ohanashi."