Kurobocchan

After five long years of being a demon and living in the underworld with Sebastian, Ciel has finally gotten to the point that he no longer can survive without some form of sustenance. So he has now had the news broken to him that he is in need of contracting to a human and will eventually – after completing their goal/final desire – consume their soul.

On top of that, Sebastian isn't very happy that he is now having to serve Ciel for eternity and will never again be completely free, nor will he ever consume another soul to satiate his own eternal hunger. Devising a plan to, not only help his Master contract to someone, but also get a little revenge of his own for what Ciel had tricked him (unintentionally) in to.