Yukako is a student in love with Koichi Hirose. At first she was very aggressive in her affections towards him, jealously attacking what she believed were potential rivals in love and even going so far as to kidnap him and threaten his life should he not return her feelings and not appreciate her efforts to "change him into a better person" – she had picked up false rumors that he was insufferable, false rumors that were spread by Josuke and Okuyasu in order to help Koichi in turning her away from him; unfortunately for them, their measures had the opposite effect.
Later in the story Yukako, still lovestruck, seemed to have learned from her mistake in trying to force Koichi. Unhappy about her unrequited love she made use of the services offered by Aya Tsuji's beauty enhancing Cinderella stand, which rendered her into a bewitchingly attractive woman in the eyes of Koichi—for a price and a certain time limit, during which she was to use a special lipstick in order to uphold the "magic" i.e. the stand's power.
(Source: JJBA Wikia)
