Age: 13

Birthday: May 28th

Blood type: O

Kozue is Miki's twin sister who feels overshadowed by his talent and dirtied by comparison with him. Kozue resents Miki's affection for Anthy Himemiya and is prone to "acting out" to grab her brother's attention, most notably by exercising loose sexual morals. Like Nanami, Kozue also seems to have an extreme brother complex. She is very protective of Miki and is the reason that he does not have a girlfriend (despite the affection of many of his schoolmates).

Kozue considers herself a "wild animal," wanting to be freed from adult rules and restrictions (in reality, she is resentful of her father's remarrying).