Author's Note: I've started another series because apparently I haven't got enough to update. This came to me after I had a Faith marathon on November 13th (two days after the news about Dollhouse hit). I'm not sure if I got the Faith-voice right, but as we've only seen empowered!Faith, I wasn't sure how loud and cocky she would be. Reviews are shiny and make me do a little dance. Also, I'm in the mood to do prompty one-shots. Any suggestions would be great.
This chapter has been edited because I'm an idiot and only realized after I first posted it that Snape taught DADA, not Potions in HBP... sorry!

A not-so-vague Disclaimer: I seriously hope a professional could write better than me (not counting the Twilight woman)… so obviously I don't own either canon.

Potions class was dragging on… Slughorn had given up on trying to teach them how to make a babbling draft and was instead making them copy out the pages of the textbook dedicated to the potion. Which was pointless and painful. It was her sixth year of Hogwarts and Faith still wasn't used to writing with a quill. Okay, so she hadn't done much general writing at her muggle elementary school… She was interrupted from her completely out-of-character, boredom-induced mental rant about writing by Snape's face looming over her from in front of her desk. Which gave her quite a shock… 'cause it's really unnerving to be interrupted from a mental rant by someone looking at you in a rather intense manner. Especially if that someone had a… intense face. Ugh, mentally she was talking like an English person. She was interrupted from her second mental rant of the lesson by the professor clearing his throat.

"What?"

"The headmaster wants to see you after the lesson, Miss Lehane"

"Huh, Albie wants to see me? I'm flattered." She joked. The professor let out a short laugh before walking away. Draco elbowed her in the ribs when the professor sat back down.

"Someone's in trouble…" He sang in a whisper.

"Someone sounds like a twelve year old girl…" She sang back.

"What did you do this time?" He asked, looking more serious.

"Hmmm… It could be they've found the bleached bones of all the house elves I've slaughtered under my bed… Or maybe they think I'm Sirius Black 'cept under the influence of Polyjuice…" She said in a sarcastic voice "I haven't done anything, idiot."

"Idiot? You know, you really shouldn't try to insult people before you've had a cigarette, it's just rather depressing."

"I'll bear that in mind." Was her response.

When the lesson ended Draco walked her over to Dumbles' office, keeping her mind occupied with a story about one of his 'conquests', as he called them. When they came to the entrance he smiled.

"If you're expelled you can live at my house… my mum wouldn't notice."

"If I'm expelled I'm going to bring you down with me." She joked and he walked back to the great hall. She took a deep breath and tied back her hair as she told the gargoyle guarding the entrance the password.

To her surprise, when she walked into the office she saw that there was another student sitting in front of the headmaster's desk.

"Morning Potter." She greeted him in a decidedly neutral way.

"Faith." He nodded to her. She resisted the urge to laugh at his attempt at looking tough.

"So, d'you know why we're here?" She asked, sitting down on the chair next to him.

"You didn't do something and try and pin it on me, did you?" He asked. She giggled.

"What would I do?" She smiled. Before Harry could respond to her, Dumbledore walked in and sat at the desk. After he greeted them both he smiled warmly.

"I've called you both here today to tell you something." He started.

'Well duh,' Faith thought.

"Something that is of great importance, given that Lord Voldemort is gaining power by the day… I have to apologise for not being honest with you, but it was what your parents wanted."

"Our parents?" Faith and Harry spluttered at the same time.

"Faith, you're Harry's elder sister."

"No I'm not… I'm an only child." Faith said slowly.

"You're adopted."

"I can't be…" She started but was lost for words.

"I'm sorry to have to tell you, but you are. Your parents had you adopted shortly before Harry was born, to keep you safe."

"Safe?" She half-choked the word out.

"They were in danger and they wanted to keep you away from it."

"It wasn't their fault." Faith had forgotten that Harry was in the room and jumped at the sound of his voice. "They thought they were doing the right thing."

"Miss Lehane, if you're going to blame anyone, blame me. I was the one who chose your adoptive parents. I didn't know what was going to happen." Dumbledore said in an even tone. Harry looked curious but didn't say anything.

"I bet James and Lily Potter would be proud of their Slytherin daughter." Faith joked.

Author's Note: I've had to skew the Buffy canon and make Faith and Buffy the same age so their new DOBs are September 14th 1979 (Faith was born on December 14th 1980 according to the Buffyverse Wiki, but for Faith and Harry to be in the same year she had to be born three months earlier.) and January 20th / 21st 1980 (The whole Capricorn on the cusp of Aquarius confuses me). As this takes place in HBP, Faith should be activated as the slayer on May 19th. (But it's September at the moment, so we've got a bit of a wait.)