I am Sebastian, the head butler of the Phantomhive household. My job is to serve a child who goes by the name of Ciel. Day in and day out I follow him by his side, making sure everything goes accordingly as planned in his schedule. I signed a contract with him, following three years ago, promising that I'd bring forth his revenge in exchange for his soul. Therefore, I trail him like a filthy dog, watching over and protecting him from his enemies.
Of course, revenge is not the only thing this demon is capable of; I have the most accurate knowledge on everything there is to know, undoubted strength, agility and flexibility, and the gifted ability to create the perfect pastry, desired by the young master. What would a Phantomhive servant be if he could not do such things? Well, I'll tell you... he wouldn't be a Phantomhive servant. Simple as that. I somehow manage to keep the household on top of things, without the aid of the other servants. It's only natural for me to do so. I guess you could say I'm simply one hell of a butler.
Although, in your present time, I'd be considered as Ciel's man-b***h. If that is what it's called, then so be it; I am one hell of a man-b***h.