Ciel (シエル, Shieru) is an android created by Zeppeli. Unlike other androids who can only say "Fuga," he is capable of normal speech, however he can understand what they are saying. After meeting Flandre in town, he helped with the upkeep in Hime's mansion, and later developed a relationship with Flandre, during the time of her repairing him.
Flandre bumped into Ciel while on a grocery shopping trip. She tried to walk away but he stops her and reveals that he's an android in poor condition who needs to be repaired. Flandre takes him back to the mansion, where he was able to get fixed.
In the middle of his repairment, he gave Flandre a sea shell and told her his story: he began as a miner in the Kingdom's deuterium mine but one day he escaped. He walked and walked until he came across an ocean, the view of which pleased him greatly. He then told Flandre that all the androids are free beings and asked her if she has seen the ocean. Soon after his repairment, Hime tells him that some major parts of him are still not corrected, if he goes back to the Kingdom, the professionals can completely restore him; if he chooses not to, then he can only function for one more year. Ciel refuses the offer and instead states that he will continue traveling; traveling has given him the sense of freedom and if he goes back to the kingdom, all of his memories will be erased.
That night, Ciel suddenly walks out in the middle of charging and went to Hime, who was awake and on guard because a free-willed android is something she's never seen. He easily flung Flandre aside, damaging her and abducted Hime, who did not resist because she knew it will be useless. Fortunately, Sherwood and Francisca came and stopped him. After analyzing his programming, they discovered that he had only been active for a very short amount of time (about 10 days in the anime/10 hours in the manga), meaning there's no way he's experienced the things he claimed to have happened. After he woke up, he was told of the news and realized what's going on. He then sacrificed his right arm for parts to save Flandre.
Later that night, Ciel went to the hospital with Hime on his shoulder confronting Zeppeli, who was behind everything. Realizing that all his memories had been fabricated, Ciel took Hime's "body"-a dummy wrapped in explosives, and self-destructs, hoping to take Zeppeli with him. Zeppeli however, survives.
- Ciel is implied to have feelings for Flandre, as she is often seen close to him and the two are very friendly with each other. He gave her a shell that he presumably found on a beach as a memento that Flandre still keeps. During his final moments, he laments his life and stated that he wants to fall in love with someone, with Flandre's image being shown which supports the theory.
- Ciel gave himself his name.