Ciel is not the only surviving Phantomhive and he is not the eldest either. His older brother, Vladimir Phantomhive, Lord of the Phantomhives, eldest son of the late Lord Vincent and the late Lady Rachel Phantomhive, is the one who makes a deal with a demon, who he let Ciel name Sebastian Michaelis. Yet even though both brothers struck similar contracts with the same demon, the son of Satan only has his sight set on the eldest brother, not only because of the Faustian contract but because the eldest Phantomhive brother is his mate and he will protect both brothers, no matter what it takes.