The manga follows Rumi Ikuno, a second-year student who transferred into Hanagaoka Private Girls' Academy. She leads a simple, oblivious life, even as she causes bewilderment and trouble around her. The manga depicts the profoundly strange girl's life that is sometimes amusing, but mostly irritating.

(Source: ANN)

Included one-shot:
Volume 4: Rumi-chan Zenya: Rumi-chan ga, Ima no Rumi-chan ni Naru Sukoshi Mae no Ohanashi (pilot)