I haven’t seen the anime yet, but I’ve been spoiled on the ending. If you do not wish to be spoiled either, then read no further.
For more information on 黒執事, see: Wikipedia’s Black Butler entry, Square Enix’s official page about the mana, Funimation’s official english page about the anime, and the unofficial fan wiki.
Short summary: After a long time of Sebastian, a demon, working as a butler for Ciel, a young child who wants revenge against the murderers of his family… the contract remains strangely unfulfilled due to events out of left field. Ciel becomes a demon, and Sebastian not only doesn’t get to devour Ciel’s soul (and Sebastian is very, very hungry indeed) but now he must remain Ciel’s butler for eternity, or at lest, gods know how long.
Sebastian is rather put out by this.
However, as there are rumors of yet another season 3, I think Sebastian will eventually regain his lacklusterness. Season 2 was all about Ciel’s lackluster; perhaps a similar character arc for Sebastian would be fitting. And thus Sebastian would, for once, not be the perfect, capable butler.
Eventually, the conflict between the newly arrogant Ciel, who seems not to realize that there’s a whole world of demons out there who’d gut him, and then even more bound Sebastian may smooth out (over many snarky bumps) to an understanding, to a holding position:
- Ciel no longer has human concerns, and can lay his desire for revenge to death if he hasn’t already. He has a new world to explore, and he does love a challenge.
- We never hear about how Sebastian become demon. There’s implications that he was bored and his life was slovenly, grabbing souls left and right; getting hold of contracts stepped up the game to dignity and strategy and, most likely, a more interesting, challenging life than he might have had otherwise.
These two will never not be rivals. But they need the other in their life to navigate the pools of chaos they’ll encounter on the other side, even if they’ll never exactly be friends—the relationship dynamic is not based on trust, but on need.
What will happen in the new world? Is there a manor house on the other side they can occupy and start over again? You need something to have a butler/master relationship to play against…