Katarin's Orthodox outfit. (Pixiv Fanbox)

She was allowed to wear Orthodox clothing as a sign of her purification after being judged by the Great Orthodox Church, but since she is no longer queen, she has taken the position of courtesan and converted it into a perverted outfit befitting of her position. The outfit is an adaptation of Kostaltyn's clothing to show off that Katarin is a courtesan owned by Kostaltyn.