The demon and the demon hunter (Sebastian x reader)

(Y/N) (L/N) is the top agent of the N.H.A.O (Non-human assassination organization) in the organization you are part of an elite team that kills Non-human things you are known for being a cold-blooded killer. But your one weakness is Mery-in you to were born on the same day and have been friends for life you and Mery-in still keep in contact after she left the N.H.A.O but you have some bad new that you have to tell her in person. But what happens when you meet the mysterious butler Sebastian Michaelis? What will happen when you have to stay at the manor for a week? Read to find out?