Koan

Koan is the youngest of the four Ayakashi Sisters and a member of the Black Moon Clan.

Appearance
Koan has wavy dark purple hair that falls down her back and dark purple eyes. She wears a pink pinstriped onesie, a dark purple tutu and dark purple heels. She also wears a black rose corsage around her neck and an identical ring on her right hand. In the crown of her forehead, she wears a purple gem encrusted with pearls.

Bishoujo Senshi Sailor Moon R (original timeline)
Koan first appeared in Act 15 of the manga, where she was in charge of Operation 001: Operation Recruit. Disguising herself as a T.A Girls Academy student named Koan Kurozuki, she recruited people to the Black Moon by foreseeing their deaths and then promising a peaceful passing if they joined her. Unfortunately, those who agreed bore a crescent sign that would then cause the bearer to spontaneously combust, as they were most likely unable to handle the power.

After finding one of the school's teachers who had suffered this fate, Sailor Mars confronted her, but was trapped in Koan's flame barrier. Though Sailor Moon used her new Cutie Moon Rod to destroy Koan with Moon Princess Halation, she was unable to break the flame barrier, and Sailor Mars was abducted by Rubeus.

Arc 1
Koan first appears in Act 1 where Hikari encounters her undercover in a candy shop. Later on, she reveals her true identity after intercepting Usagi and Chibiusa and engages in a battle with the Sailor Senshi. She's almost killed by Sailor Moon's Moon Princess Halation but is saved by Sailor Stellar.

In Act 2, she identifies Hikari as being the Sailor Soldier who saved her, and vouches for her to be kept alive. Later on, when her and Hikari are devising a plan to attack Tokyo, she questions who Hikari is and where she comes from. She finds out that Hikari is from "The Real World" and that in her reality the Black Moon Clan are nothing more than works of fiction.

Trivia

 * Koan is named after Kooankou (紅安鉱), a mineral that is also known as Kermesite.
 * It is unknown in Pretty Soldier Sailor Stellar if the battle shown in Act 1 was the Sailor Senshi's first encounter with Koan. It is indicated that it isn't, but then begs the question of what happened during Koan's first appearance in the original timeline, since she's shown to have survived.