Sebastian takes on the appearance of a tall, handsome adult with black hair, reddish brown eyes, pale skin, and black fingernails. The back of his left hand contains the mark of his Faustian contract with Ciel Phantomhive.

Ciel is a short, slight teenage boy with grey-tinged,[12] blue-black hair and rich peacock-blue eyes.[13] As described by his tailor, Nina Hopkins, Ciel has a well-proportioned body: His arms and legs are thin, his shoulders slim, and his waist narrow.