"Ciel" looks identical to his brother and they have been stated to be mirror twins, but unlike Ciel he does not bear a Faustian contract mark on his right eye. Another noticeable difference is that where Ciel's bangs curl to the right, "Ciel's" bangs curl to the left.
He is an individual who exudes confidence and remains unruffled, even when accused of being an impostor.
When appearing as a younger child, "Ciel" has a notably more confident aura than his brother; he is usually seen smiling widely, laughing and playing with Lizzy.  It is also apparent that "Ciel" did not suffer from debilitating asthma  as his twin once did.
Flashback Sequences: An Overview
Throughout the manga, "Ciel" can be seen appearing in numerous flashback sequences, though his appearance may be (as intended by the author) confused with Ciel Phantomhive. 
It can be presumed that "Ciel Phantomhive" was the child sacrificed on January 1887 (the day his brother Ciel made a contract with Sebastian Michaelis) though the details of his revival have yet to be explained in the manga.
Among other differences, "Ciel" can be distinguished from his brother by the bruise under his left eye and his top button which is done up. In contrast, Ciel has no bruise under his left eye and his top button hangs loose on a string.
He is seen comforting his brother during their kidnapping, offering him support in times of anxiety. 
Blue Cult Arc
Later, Ciel Phantomhive and Sebastian Michaelis also enter the manor. "Ciel" hears them, and descends the stairs, to their collective shock. He scolds a dismayed Ciel for getting drenched, and assures him that he will never leave his side again, and that he has come home. When Finnian states that it is impossible for there to be two Ciels, "Ciel" asserts that he is real. Finnian adds that he knew something was wrong when "Ciel" came home, and calls him an impostor. Amused, "Ciel" declares that the head of the Phantomhive house, Ciel Phantomhive, is actually he.
"Ciel" muses that this is the first time he has actually met Sebastian. He promptly asks him how dare he "do that" to him on "that day". Sebastian affirms "Ciel's" statement that he is "Earl Ciel Phantomhive", to the servants' disbelief. At that moment, Tanaka arrives at the staircase and addresses "Ciel", stating that he was not in his room when he brought his tea. He reveals that he knew all along that there were two Ciels; twins in fact, to the bewildered servants.
An amused "Ciel" chides Ciel for confusing the servants by impersonating him. He adds that Tanaka told him that he used losing everything in the the fire as an opportunity to hide the fact that he was a twin and calls Ciel a naughty boy for doing so. Ciel is hesitant when "Ciel" asks him why he made such an outrageous lie and states that he will not be angry with him. Ciel, then, mutters that he is "the spare" to "Ciel Phantomhive", heir to Earl Phantomhive.
- ↑ Kuroshitsuji manga; Chapter 85, page 22
- ↑ Kuroshitsuji manga; Chapter 129, pages 37-38
- ↑ Kuroshitsuji manga; Chapter 129, pages 36-37
- ↑ Kuroshitsuji manga; chapter 10, pages 17-18.
- ↑ Kuroshitsuji manga; chapter 129, page 28.
- ↑ Kuroshitsuji manga, chapter 11, pages 17-18. [first appearance]
- ↑ Kuroshitsuji manga, chapter 90, pages 17-19.
- ↑ Kuroshitsuji manga; Chapter 129, pages 15-16
- ↑ Kuroshitsuji manga; Chapter 129, pages 27-38
- ↑ Kuroshitsuji manga; Chapter 130, pages 4-9
- ↑ Kuroshitsuji manga; Chapter 130, pages 15-19