Supernatural Little Sister

"Say yes, Dean."

This is based off of Season 5 Episode 1, "Sympathy for the Devil."
Enjoy!

Allison: 18
Dean: 27
Sam: 24

"What do you mean I'm Michael's sword?" Dean growls at Zachariah who stands before the Winchesters with his angel entourage.
"You're his vessel, Dean. Actually, the vessel." He says smugly.
"I'm not signing up to be some angel's condom. No, thank you." Dean says.
"Joking. Always joking." Zachariah sighs at Dean. "No more jokes." Zachariah snaps his fingers at Sam. Sam falls to the ground with a crack, emitting a terrible scream.
"You son of a bitch." Dean scowls at Zachariah as Allison runs to Sam who writhes in pain on the floor.
"Stop mouthing off or I'll break more than his legs." The angel says cruelly. "Dean, Michael will take his vessel and lead the charge in the final battle. It is written; it must be done."
"There's gotta be a reason why you're not just taking me now. Michael needs my permission to hop inside my meat suit."
"Unfortunately, yes. But Dean, it's the right thing to do!" Zachariah yells.
"Is it? How many innocent people are gonna die in the crossfire of this final battle, hm? 5, 10 million?" Dean says.
"Probably more. You know how many will die if we don't beat Lucifer? All of them. He'll roast this planet alive." Zachariah says. "Do the right thing, Dean. Say yes." Dean looks to the floor and then back up at the angel.
"No." Dean says firmly.
"Dean, Dean, Dean." Zachariah tisks his tongue at Dean and then cocks his head sadly at Allison. Allison pulls away from Sam and grasps her stomach.
"I don't feel good, De—"An agonized scream rips out of Allison's throat as she collapses on the ground. She vomits blood up into her hand and whimpers shakily.
"What the hell did you do to her?" Dean yells.
"Poor little Allison's stomach ruptured. You can still save her, Dean! Just say yes." Zachariah says as Allison cries out in pain. Dean looks to his little sister and runs his hands through his hair nervously. She shakes her head at Dean as she coughs up more blood.
"No." Dean says shakily and Zachariah sighs.
"Come on, Dean. You're really that selfish to let your baby sister die when you could just say yes and have it all go away?" Zachariah jeers and Dean looks to the ground, his confidence in shambles.
"He said no." Sam growls.
"Leave us alone." Allison gurgles.
"Shut up, swine." Zachariah says, throwing them against the wall. "We know your friend Bobby is gravely injured. How about this? You say yes and we'll heal him. You say no, he'll never walk again."
"No." Dean says after a tense pause.
"Alright. How about we remove the inoperable brain tumor pressing down on your occipital lobe?" Zachariah smiles as Dean clutches his head because of the overwhelming pain. Dean's eyes dart around the room, his vision blurred.
"No." Dean clenches his jaw as he holds the back of his head tenderly.
"Fine. Let's see who'll last longer without lungs. Allison or Sammy?" Zachariah taunts and then snaps his fingers. Dean's siblings desperately clutch their throats, gagging and gasping for air. "My money's on Sam." Zachariah smiles and crosses his arms over his chest. Dean falls to his knees in defeat.
"Are we having fun yet?" Zachariah says smugly and saunters over to Dean. Dean winces as Zachariah grabs his face aggressively. "You're going to say yes, Dean."
"Just kill us." Dean whispers.
"Kill you? Oh, no. I'm just getting started." Zachariah says. Suddenly, a white flash of light blinds and stuns Zachariah; Castiel has killed one of Zachariah's companions. Castiel promptly moves to the other angel and stabs his angel blade through its neck. Zachariah stares, mouth agape, at Castiel.
"Put these kids back together and leave." Castiel threatens. Zachariah scowls and then looks to the Winchesters sputtering on the ground. Wings flutter and Zachariah vanishes. The Winchesters relax and take in a deep breath. Sam helps Allison up off of the ground and Dean checks in with both of them.
"You need to be more careful." Castiel warns.
"Yeah, I'm starting to get that. Your frat brothers are bigger dicks than I thought." Dean says.
"I don't mean the angels. Lucifer is circling his vessel and once he takes it, those hex bags won't be enough to protect you." Castiel approaches the Winchesters and one by one places a firm hand on their chests, rattling their bones with astounding power.
"What the hell was that?" Dean groans.
"An enochian sigil. It'll hide you from every angel in creation, including Lucifer." Castiel says.
"What, did you just brand us with it?" Allison asks sassily.
"No, I carved it into your ribs." Castiel says succinctly.
"Well...thanks." Sam says hesitantly.
"You are welcome." Castiel nods. "You're safe...for now."
"Real comforting, Cas." Allison says and Sam gives a weak laugh. Castiel nods, not understanding the sarcasm, and shows the Winchesters the way out.