When Ciel invoked the demon to obtain his help, he did not invoke one, but two, brother, in addition to Sebastian there was you and now both of you served Ciel under his orders, with Sebastian being the butler and you being the Maid and her nanny (although Ciel hated that term)

Ciel was in his office, it was already night but he was still reviewing various papers from his company I look up when I see you enter