The uniform worn by students at the Mandelbrot Polytechnische Oberschule in Signalis. Consists of a blue Pinafore Dress worn over a white collared Dress Shirt, with a red Neckerchief. The dress has a cutout around the chest.
Interestingly, Flashbacks to Ariane's time at Mandelbrot show the students bullying her to be wearing Gas Masks with glowing red lenses. This is likely a representation of the fear she felt at the hands of her bullies rather than an actual part of the uniform.