|Birthdate:||June 6, 1983|
|Age:||22 (First Series)|
Kaoru Mitsuki (御月 カオル Mitsuki Kaoru) is the female protagonist of the series, an aspiring artist who's always having trouble making money. Though learning of the Makai Knights and the Horrors, Kaoru learns that her destiny was intertwined in the conflict since her childhood. Kaoru is portrayed by Mika Hijii (肘井 美佳 Hijii Mika). As a child, she is portrayed by Kanami Katchi (甲地 夏波 Katchi Kanami).
Born to her parents, the famous artist Yuji Mitsuki (御月 由児 Mitsuki Yūji) and Karin Mitsuki (御月 かりん Mitsuki Karin), Kaoru was six years old when she is found by Barago who converted her into a gate for his plan to bring Messiah into the world.
Kaoru gets a break the day she is able to present her art at the gallery of Tasuke Taniyama, unaware that he is possessed by the Horror Anglay who intended to devour her before Kouga arrived and bought her painting to have her take it to his manor while he attempts to slay the Horror. However, returning to the gallery as the fight reaches its climax, Kaoru is splashed with Anglay's blood with Kouga sparing her life to find a way to save her life while giving Zaruba and the Eastern Watchdogs the notion that he intends to use her as Horror bait while keeping the secret of her condition from her.
Kaoru eventually was evicted from her apartment and temporarily freeloaded at Asami's place. After Kaoru's bad cooking gave Asami food poisoning, she moved into Kouga's home. She literally took Kouga's words of staying close as an excuse to move in. Kouga wanted her to at least earn her keep, but her cooking was so horrible that Gonza became ill.
Kaoru has feelings for Kouga as well, but was devastated when she found out Kouga used her as Horror bait, even though Kouga actually never did it until the occasion where she found it out. Kaoru always seem to manage to involve herself with a Horror all on her own, and that's why Kouga always says she's an unlucky woman. For her protection, Kouga placed a special ring created by Zaruba in one of her fingers, allowing him to always locate Kaoru's position when necessary and be alerted if a Horror is close to her, though she forced Zaruba to take it back when the truth came out. Eventually, Kouga managed to save Kaoru's life with the Barankas fruit.
Kaoru also learns of his father's ties to Kouga's father Taiga, finding the picture book from her dreams that her father wrote let never finished the final age. As Barago's scheme is nearly complete, Kaoru's nature as Messiah's gate begins to manifest as he kidnaps her. Trusting her to Elda, Barago conveys to Kaoru his life story and the fact that she has also been possessed by Messiah herself at times during their meetings. Rendered in a comatose state as Messiah begins to enter the human world, Kaoru played a role in having Kouga defeat the Horror and bring him back to their world. Soon after, Kaoru presents Kouga the finished the last page of the Golden Knight and the Black Flame book before she leaves for Italy.
- Mika Hijii also portrayed Miyuki Yoshinaga/Orchid Undead from Kamen rider Blade.