The second costume of Nijisanji's Matsukai Mao, as seen on Twitter.
It consists of a short frilled black collared dress with long sleeves a red ascot and a white and a black layered miniskirt underneath, which is then used as the basis for either a maid costume, or a military uniform, with each of its associated accessories being toggleable, allowing her to mix and match elements from both, alongside additional accessories.
The maid version adds a maid headdress and white frilled waist apron, while the military version adds a black military hat and a double-breasted black capelet with epaulettes and an aiguillette. Both versions feature mismatched black thighhighs with a frilled lace thighhigh and a garter strap on one leg and cat ear thighhigh on the other. She also has an optional medical eyepatch, cat ears and a tail and low wings demon wings.
This tag implicates matsukai_mao (learn more).