Kozue Kaoru is a student at Ohtori Academy and the twin sister of Miki Kaoru. She is introduced as a seemingly gentle and soft-spoken girl who plays the piano, but her outward grace quickly reveals a more complicated and cynical inner world. Kozue and Miki are known as the academy’s “prodigy twins,” having both shown early musical talent, though Kozue has since stopped performing publicly.

Kozue’s personality is marked by a sharp, manipulative edge and a deep-seated bitterness. She often uses her innocent appearance and flirtatious demeanor to get what she wants, particularly from men, whom she treats as disposable. Unlike her brother’s idealistic and earnest nature, Kozue is pragmatic, resentful, and prone to emotional provocation. She frequently mocks Miki’s romanticized view of their shared past, especially his memory of listening to a piece of music as children, which she reveals was never a pure or happy moment for her. Her behavior stems from feeling overshadowed and confined by Miki’s perception of her as a fragile, perfect muse.

Motivationally, Kozue seeks to dismantle the illusion of purity that Miki and others project onto her. She desires control over her own identity and is willing to engage in self-destructive acts to prove that she is not the innocent girl her brother remembers. Her participation in the duels for the Rose Bride is less about winning Anthy or achieving any ideal of “revolution” and more about hurting Miki, asserting her independence, and testing the limits of how far she can push against the school’s systems. She also envies and mimics the more overtly powerful student council members, particularly Juri Arisugawa, but lacks their discipline.

In the story, Kozue serves as a foil to Miki and a darker reflection of the series’ themes about adolescence, memory, and identity. She becomes a Duelist representing the Black Rose arc, manipulated by Souji Mikage, who preys on her resentment. Her key relationships revolve around her twin. She shares a deeply entangled, borderline incestuous tension with Miki—not necessarily physical, but psychologically co-dependent and rivalrous. She also interacts with Anthy Himemiya with suspicion and occasional cruelty, viewing her as another girl playing a role. Kozue briefly pursues Touga Kiryuu, seeing in him a cynical counterpart, but he ultimately dismisses her. Her most honest exchanges are with Utena Tenjou, whom she both respects and resents for her straightforwardness and refusal to play games.

Developmentally, Kozue moves from a position of hidden spite to open confrontation. During the Black Rose saga, she duels Utena while wearing a rose-colored pendant that amplifies her anger. After losing, the pendant’s influence is broken, and she returns to a quieter, less destructive state—though not completely reformed. In the series’ final arcs, she appears more subdued, still distant from Miki but no longer actively scheming. The implication is that she has accepted a degree of separation from her brother and the idealized past, though her cynicism remains.

Notable abilities include her skill at the piano, though she deliberately plays off-key or stops mid-performance to unsettle listeners. She is also a capable duelist, wielding a sword with erratic but effective aggression. Her true ability lies in psychological manipulation: reading people’s desires and insecurities, then weaponizing them with feigned vulnerability. Unlike many duelists, she rejects the romantic or heroic framing of the duels, making her one of the most grounded yet unsettling characters in the series.