The elementary school girl Rumika, who loves her big sister dearly, has a secret she can't tell anyone. That is, her beloved sister is a complete slacker at home and has a hobby of cosplay. Rumika becomes closer with her cosplay friend Aira, and although she finds her sister uninteresting, she takes good care of her lazy sister every day. Even in their usual routine, changes start to occur little by little... A quirky sisterly living comedy, concluding in volume 3♪