Height 165 cm (5'5") Ciel is first presented as a senior attending the same school as the main protagonist Shiki Tohno, where she is the president and only member of the tea ceremony club, and also good friends with Arihiko Inui, Satsuki Yumizuka and Shiki himself. Her outward demeanor is that of a calm, friendly, and peaceful person. However, Ciel's true character is later revealed as the story progresses. She is a member of the Burial Agency, a secret organization within the Catholic Church made up of skilled assassins, feared even within the Church itself, known for showing no mercy and willing to do whatever it takes to get their task done even to the point of using forbidden magics and creatures. Her objective in Tsukihime is that of hunting down the heretic vampire Roa, which while being a direct order from the church is also her own vendetta. In Melty Blood she has been ordered by the church to hunt down Roa.

Spoiler

Ciel (whose real first name is Elesia) was a normal individual born in France to a French father and an Oriental mother. However, unlike those around her, Elesia had a high magic potential, and it was this rare characteristic which ultimately put Roa inside her as his 17th host body after his 16th host body was killed without having chosen his next host body. In the process, Ciel became a vampire and killed everyone in her village, the massacre only ended when Arcueid Brunestud arrived and killed her, fulfilling her duty of killing Roa whenever he reincarnates. However, unlike previous hosts, Ciel returned to life after Roa had moved on to a new host. The secret Vatican agency known as the Burial Agency captured her, and over the course of a month she was killed repeatedly by the Church, only to rise again on every occasion, because as a host of Roa while Roa was also inhabiting another, it was impossible for her to permanently die until Roa was killed. Despite their usual views on sorcery, vampires, and the like, the Church decided to use her abilities as a member of the Burial Agency, her main desire and mission being the elimination of Roa to end her eternal existence.