The Girl and the Devil (Supernatural)

Chaper 1

"Dean! I'm really not such a little girl anymore!", Amondine groaned and crossed her arms in front of her chest. They refused to take her on a hunt yet again, although she had passed all of their trainings, all of the lessons and every hunt she had been on so far.
"You are our little sister! We don't want you in danger.", Sam replied and she just rolled your eyes. She wasn't really their sister, their parents had been hunting partners and first John and then Bobby had taken care of her when her parents had died during a case.
"Please! It's so boring to be here all alone!", she complained trying to change the tactic.
"We need you here for research Amo... look, I'm sorry, okay? But we really are worried and need you here...", Dean spoke and hugged her before leaving towards his car. Sam just nodded before following his brother leaving the younger girl all by herself. She groaned and took a deep breath accepting her faith of having to stay behind, so instead of complaining she decided to start her research.
After all the time that she already lived in the bunker now she still was impressed and surprised by its size and amount of furniture and especially books. On her way to the library she heard book pages being turned and frowned.
"Great.... now I'm hallucinating...", she mumbled to herself and switched on the light stopping midway into the room. Someone was standing there. Someone other than Castiel. She backed away lightly and placed her hand on her angel blade.
"Who are you? And what do you do here?", she asked sternly sounding way more confident than she actually was.
"Well hello there!", the unknown male replied and tilted his head at her. "Who are you my dear?"
"I asked first. Tell me who you are.", she shot back knowing all too well how childish that made her look.
"I'm Lucifer. And you sweetheart must be Amondine? The little sister?", he asked and she opened her eyes widely.
"H-how do you know? How did you get in here?"