She is generally seen wearing Senketsu, which can change form. While in a normal state, Senketsu is essentially a serafuku. The top is somewhat short, with suspenders between it and the pleated skirt. Ryuuko's midriff and navel are shown.
While in a transformed state, Senketsu changes dramatically. The top and skirt get dramatically shorter, exposing Ryuuko's underboob. Somehow, Ryuuko also winds up wearing thigh boots.
Matoi Ryuuko's sukajan is rather well known and has its' own tag on pixiv despite only making brief appearances in the first and last episode of the anime due to her swearing it off in favor of wearing Senketsu.
