Before demons were called to make a contract, two demons so young that even when before they went separate ways, they were close friends.
A small girl lived on her own with no family, but a small shadowy figure came by.

??? -"Are you alright?"

???-"Yea. But who are you?"

The boy seemed to smile and helped the girl up from the cold ground.

???-"My name is Sebastian. What's yours."

???-"I don't have a name."

Sebastian-"Oh well I'm gonna name you Stella. It suits a demon like you, wait your a cat right?"

Stella-"Yes. Thank you for the name though Sebastian. What are your?"

Sebastian-"I'm a raven. But not as strong as every other demon who do fights."

As the two held hands while running from everything, they found a empty house and lived together.
As years have past, they were not longer teens, but adults. The more they grew up, the more they were separated. More arguments were made, both went different ways, and never spoke to each other.
When Stella was gone, both couldn't stop thinking about each other, that Sebastian had to erase her from his memory by signing a contact to a young boy held captive in a cage, begging for help.
The thought of him doing that killed Stella on the inside and did the same, but her contract didn't last. She was a free demon once again, but her main goal was to meet Sebastian before one of them dies.

9 years later~

Stella was heading to England to probably live as a regular civilian. A civilian who tries to make money, not kill anyone, create mischief, and so on.
But everytime she tries, she always ends up bumping into police men, and running away with a laugh. Now that she learned a few English words, she was now use to speaking that way.

Cop-"Come on down from there Missy!"

Stella-"Oh but copper, don't see I'm just hungry and well a lil bit of a troublemaker."

Cop-"This is your last warning. Get down or beheaded."

??? -"I got it from here, thank you."

Cop-"C-Ciel, the Queen's guard dog!? We will let you be."

???-"Thank you gentlemen, here is a token for cooperating with Lord Phantomhive."

Ciel-"Sebastian, get her down and bring her to me."

Sebastian-"Yes my lord."

As the name struck Stella as a ton of bricks fell on her, she quickly ran across different branches of get away from him. But he stopped her dead, and stared at her for awhile. After he heard his name being called, he got Stella, and jumped down with a smile.
He apologized too his master Ciel and walked back with him to the mansion. As the three returned to the mansion, Sebastian put Stella in a different room, and did what he usually does. Be a Butler.
When Stella was held captive in the room, Sebastian unlocked it from the outside and let Ciel and himself in.

Ciel-"So your name is Stella, you've been stealing from almost all people in England, you haven't been here long, and yet I get informed about a girl with yellow eyes from the Queen herself?!"

Sebastian-"My lord, a cat does what it does to survive."

Ciel-"Wait cat? Like as a demon cat?"

Sebastian-"I'm afraid so. If you look closely her teeth, they aren't like ours. She still is in morphing to a human stage."

Ciel-"I see. Maybe I get a good use of her while she's here working for me."

As Stella was listening carefully, she got food from them, and a job as the dog watcher that always needs attention.
When days have past, Stella was human and was able to morph into her demon self on command. She didn't make a contract to be second demon by Ciel's side, but she did agree too work without getting any suspension from the cops.