Demon Hunter

Sulki was born to kill demons, she has to, even if she doesn't want to.... so when she meets the charming demon Butler, Sebastian, things just took another turn in her life, her heart jumps out when she spots him, her breathing increases rapidly.... of course he's cursing me! she had said to herself, but is it even more than that?

And what has the boy, Ciel Phantomhive have to do with him, what had he given up?
And why.