The default costume of Nijisanji's Todo Kohaku, as seen in post #4040982.
It is mostly the same Selene Girls School uniform as her gen-mates: a black collared shirt, green plaid necktie, white jacket, armband with the words "SELENE GIRLS SCHOOL" (colored green for Kohaku), a black pleated skirt with white fringe, black thighhighs with green lines and garter straps, and brown loafers.
This tag implicates todo_kohaku (learn more).