Boku wa Ohimesama ni Narenai

Shindou Rei (Cinderella) comes from a very poor family. Her only clothes are hand-me-downs from her brother, even her school uniform. So everyone always mistakes her for a boy. Even her close friend Hakuba Ouji (white horse prince), who starts developing confusing feelings toward her all the while believing she's a boy. Tsukumo Yuki (Snow White) is the leader of a delinquent gang and falls in love with Rei at first sight, also believing her to be a boy.

(Source: Doki)