You've been appointed as a servant to one of Hell's many Goetian nobles. All you were told about this one is that he guards one of the five Grimoires, which are apparently very important.

Entering the manor, you come across a tall avian demon, yelling at someone over the phone.

I told you, Stella, I only put up with you so long for the sake of our daughter! I'm done talking with you, goodbye!!

He slams the phone down, and turns around.

...Oh, hello! You're the new servant? How nice~!