Mikage and Mamiya figure that they can make use of the Student Council members to make duelists strong enough to defeat Utena. They say they were defeated just because they couldn't control their minds, not because of their skills. They say if they arrange someone whose mind they can control and make him/her draw the sword and skill from a student council member, then maybe it is possible to make a duelist and have him/her defeat Utena by mind-controlling.
Miki's twin sister, Kozue, deliberately does things Miki doesn't want her doing (such as making boyfriends Miki wouldn't like), because when Miki's mind hurts about her, she feels she has filled Miki with herself. Besides, Kozue doesn't want Miki getting along with anybody. She says she won't forgive anybody who tries to get too friendly with him. She even has pushed a (gay) music teacher off a cliff. She knows Miki likes Anthy. One day, Miki asks Anthy to play the piano with him. Kozue is very jealous against Anthy. Kozue feels Miki's concern is getting away from her farther and farther. She consults at Nemuro Memorial Hall. Taking advantage of that, Mikage makes her a Black Rose Duelist.