In the last moment of Ciel's life an angel appears.
The last moment as Sebastian holds the trembling boy in his arms, dips his head to taste the soul from mortal lips. It is strong and heady, spiced with pride and cruelty, sweet with honour and the smallest hint of kindness almost lost under the spice. Sebastian is hungry, it has been so long, too long, he never thought the contract would last these seven years. But the wait was worth it for the soul has ripened, and he is ready for the feast. And an angel appears, sword like sunlight sliding between Sebastian and his prey, prising them apart.
'Leave him be, foul beast,' the angel says and Sebastian, still caught in his mortal role, raises an eyebrow instead of snarling.
'He is my legitimate prey,' he says, voice soft and reasonable but on the edge of a growl.
'For your kind there is no legitimate prey. What the Lord made belongs only to him.' Sebastian pounces, aiming for the wing joint and meaning to rip it, but he is weakened from starvation and the sword flicks out before he can avoid it. He falls, a slice across his chest weeping blood and ichor as his astral body takes the blow along with his flesh. 'And you will never prey on His children again,' the angel finishes.
Sebastian crouches, teeth showing and pupils narrowing, options running through his mind in a split second. If he fights he will lose, if he runs he might survive. Survive to feed on those souls too weak and foolish to flee, to lick up ghosts worn down by ages. Survive to live on dregs. And all his plans are dust, the meal he had counted on to restore, to enhance, his strength is about to be snatched from his jaws. No other demon would have done it, but angels are bound by no rules save the will of God. The sword is about to strike, Sebastian tenses to flee.
And Ciel steps between them, arms outstretched.
'Just what,' he demands, lordly outrage rolling off every syllable, 'are you doing to my demon?'
Sebastian's lips twitch from snarl to grin. Oh, that's his young master, facing down an angel with such arrogance that he can taste it already. The angel looks down at Ciel with eyes like chips of ice. 'I am saving you soul,' says the angel.
'Are you?' says Ciel contemptuously. 'And what right do you have to do that? Sebastian has worked long and hard for this soul, do you think you can swoop in and steal it from him now? Are you an angel or a bandit?'
The angel stares, mortals are not meant to answer so. Sebastian laughs, even as he presses a hand to his wound, and the angel's gaze goes to him, goes cold, but Ciel stands between them and the angel dare not strike.
'Your soul belongs, now and always, to God,' says the angel.
Ciel snorts. 'If He cares so much for me He should have answered seven years ago when I cried out to him. But He was not the one who rescued me. This soul is mine, and I may choose who gains it.'
'He is correct,' says Sebastian. 'Humans were given free will and you may not deny him his.' The angel glares at Sebastian as he offers it a smug grin, but it looks uncertain too. Perhaps unclear on its instructions. 'Would you like to go back to Heaven and ask what to do now? We can wait.'
'He'll probably come back with a whole host of angels if we wait for him to come back,' says Ciel, kicking idly at nothing at all. 'These angels don't seem like honourable creatures.'
'No, I'd have to agree that they don't,' answers Sebastian.
Both of them look at the angel, smirking. It shakes its beautiful wings out and sighs. 'I cannot save you against your own will,' it answers. 'Is this truly your final answer?'
'It is.' Ciel's voice is perfectly steady.
'Then I am sorry,' whispers the angel, it bends forward to kiss Ciel's forehead. Ciel scowls and ducks away the way he would from a relative who tried to do the same. His hand flaps to shoo the angel on its way.
With the angel gone Ciel looks smaller, less certain. Sebastian snakes an arm around his shoulders and pulls the trembling body flush against his own. 'So you were afraid,' he says.
Ciel leans into him, seeking comfort from a predator seconds away from eating him. 'Fear is no excuse. You have not cheated me, your service has been impeccable. I shall not rob you of your wages.' He pauses, looks down to the blood and ichor staining his coat. 'Are you hurt?'
'A little. Nothing a good meal won't fix.'
Ciel is shivering and smiling at once, ephemeral affection in his eyes. 'Then you should eat.'
Sebastian slides his fingers under Ciel's chin to tilt it up, yet still hesitates. What words are there to say before the end? Goodbye is only a contraction of God be with you. Farewell useless when Ciel will not.
In the end there is nothing and the demon simply bends his head to the vessel he holds and drinks deep.
Note: I had to edit the ending because it turns out there are no synonyms for goodbye that both sound right and don't mention God.