Cooan

コーアン

Cooan is the youngest of the sisters (the oldest in the dub) and possesses the attack "Dark Fire" ("Ice Fire" in the dub). She serves as a counterpart to Rei Hino. Her name is an abbreviation for kouankou, the Japanese term for kermesite.
In the manga, Cooan tells Rubeus that she senses someone kindred to fire, like herself, who could be persuaded to join the Black Moon. Rubeus assigns her "Code001, Operation Re-cruit" to convert humans to their cause. She poses as a student named Kurozaki Cooan at the T*A Girl's Academy, where Rei Hino attends, and becomes the leader of a paranormal club called the Black Moon. The leader of another supernatural club on campus is disturbed by how cold Cooan's hands and eyes are, and a black saucer-shaped object flies away after she leaves. Rei later has a nightmare about Cooan using her powers to burn a child's body. At the school's culture festival, she sets up a booth predicting how and when her clients will die, but when Rei appears, she tells her that everyone must die, though those who follow the Black Moon will die better. After Rei uncovers droids disguised as nuns, she transforms into Sailor Mars and defeats them, at which point Cooan reveals herself. In the ensuing battle, she blasts Sailor Mars with fire, and, in retaliation, Sailor Moon and Tuxedo Mask kill her using the Cutie Moon Rod. Mars, who was still trapped in Cooan's flames, is then abducted by Rubeus.
In the anime, Cooan is, like all her sisters, very vain about her appearance, to the point of swearing death upon anyone who smudges her makeup or ruins her hair, and she relies on her charms to get what she wants. She believes that she and Rubeus are in a relationship and competes with her sisters for his love. However, after giving him a gift of cologne, he cruelly crushes it in front of her and tells her that her next mission will be her last if she fails him. While surveying the Hikawa Shrine for Chibiusa's appearance, she appears condescending toward the relationship Rei and Yuuichiro share and often compares them unfavorably to her perceived strong relationship with Rubeus. She later gets caught up in a discussion with Rei and Usagi when Rei claims that the most important thing in a relationship is believing in and loving the other person, and Koan disagrees, claiming it only matters how much the other person loves you. Her beliefs are put to the test when Chibiusa finally arrives and Cooan goes to kill her. Yuuichiro and Rei (as Sailor Mars) both get seriously hurt trying to protect each other, which surprises Cooan because of how she had perceived the two of them before. She ultimately fails to kill Chibiusa, and Rubeus appears to evaluate her. She begs him for help, believing their love will be enough, but he tells her he has no use for her anymore and that he never loved her. He gives her a time-bomb and tells her to kill herself and the Sailor Senshi, then abandons her. Before she can use it, the other Sailor Senshi arrive and knock the bomb away from her, where it explodes harmlessly in the sky. Cooan finally starts attacking everyone in a blind rage, believing she has nowhere left to go, but Sailor Mars, after getting hurt protecting Cooan from the other Senshi, convinces her that she can have a second chance. Sailor Moon then purifies her with the Silver Crystal, and she becomes a normal human woman. She later talks her next oldest sister, Berthier, out of killing herself and the other Senshi after she too is discarded by her sisters and Rubeus, and later convinces Petz and Calaveras that they too are being used.