Sebastian is Ciel Phantomhive's devoted butler, holding a strong sense of duty to his master and his family.  He follows him faithfully and carries out Ciel's every order, while ensuring that everything runs smoothly in the Phantomhive household.  He never sleeps, as watching sleep is a luxury for a demon, and thus often carries out Ciel's tasks at night.  One of his notable traits is that he always responds to every order or demand from Ciel with the phrase, "Yes, my lord."