The New Demon In Town (Black Butler)(SebastianXDemonReader) [Editing]

Y/N is a Cat demon.
She was in the woods until she meet Ciel and Sebastian.
They asked her if she has a place to stay which Y/N answered with a no.
Ciel made a a small deal with this girl.
If she works for him she could stay at his manner.
Of course the girl said yes.
Yes I know she's a demon but she can still die. There are other demon's and grim reaper who could try and kill her.
After a couple of months Y/N and Sebastian started to be more then friends...
You could say lovers...
But what happened if someone tries to steal
Y/N.
What will Sebastian do...