Ciel voiced by Rie Tanaka, is a human and former Reploid researcher that worked for Neo Arcadia. When Mega Man X disappears eight years before the events of Mega Man Zero begins, Ciel creates Copy X to replace him. [1] She was genetically modified for an unknown purpose before her birth, which is what allows her to attain such a high level of knowledge at such a young age. Additionally, one of her ancestors, another female scientist, was apparently directly responsible for the creation of the original Mother Elf, from which all other cyber elves were spawned.

However, when the Neo Arcadia government begins oppressing and executing Reploids to solve their energy crisis, Ciel migrates with Reploid refugees to a ruined city. Knowing they were being falsely accused, she decides she can not stand by helplessly, and she soon becomes somewhat of a mother figure to many of the Reploid refugees, particularly a young girl she named Alouette. She eventually finds that her only hope is to uncover a legendary hero that most people didn't even believe in anymore: the legendary Maverick Hunter Zero. She seeks for his resting place and eventually found it, though it takes the sacrifice of one of her Cyber-Elves, Passy, to wake him up.

Throughout the games, she continues to help the Resistance, and support Zero as he carries out his missions. After the fall of Ragnarok and the death of Zero, she resolves to keep an eternal peace between humans and Reploids that Zero had been trying to create.