A costume belonging to the fictional idol group Kamiha☆Magica in Magia Record: Mahou Shoujo Madoka Magica Gaiden, first introduced in its gag comic, Magia Report (pool #12770). See post #3853578 for designs.
It consists of a white shirt with center frills, a collar and short sleeves (tied and puffy for most members, though Rena wears pleated ones instead), a neck ribbon, a gingham underbust corset with a yellow flower symbol (or rather a blue star in Kuroe's case), a pleated gingham miniskirt with frills and a back bow, white gloves, white legwear of sorts (see below for exact types for each member) and heeled mary janes with bows. The color of the outfit depends on the member.