Requested by @allofthelxghts. This takes place in Season 4 (and partly 1) of Teen Wolf. I don't know if this is exactly how you wanted it, but this is what I did anyway.
"So what's the reason you're adopting her?"
"We can't have kids of our own."
"And Y/N will be in good hands with you."
"We promise you, Mr. Winchester. If you sign the papers, Y/N will be our daughter and we won't let anything harm her," Melissa said.
Dean hesitated, before signing the papers. He didn't want to give you away, but he had to keep you safe. You were only six months old, and the demons had already heard of you. He couldn't keep you.
Dean called Sam to bring you into the room. Dean took your sleeping body, looking down at you one last time. Then he handed you to your new parents.
6 years later
Turns out, Melissa and Rafael were wrong. They could have a baby. Melissa had just given birth to a beautiful baby boy.
"Y/N, say hello to your new brother," Rafael said.
"Hi, Scott," you waved at the sleeping baby.
4 years later
You were ten years old when you parents called you into the living room.
"Y/N, sweetie, take a seat," Melissa said.
You sat on the couch and asked, "What's wrong?"
"Before we tell you, you have to know that this doesn't mean we love you any less, okay?" Rafael said.
"Okay," you said, confused.
"Y/N, you're adopted."
And with those words, your heart shattered into a million pieces. You started tearing up, and Scott, who was sitting in front of the TV watching cartoons, got up and gave you a hug, trying to cheer you up.
"I still love you. You're still my big sister."
"And you're still our daughter."
5 years later
He was drunk again. Your dad was drunk. You didn't really notice until you heard a bang at the bottom of the stairs.
You left your room to see what happened and saw Scott at the bottom of the stairs.
"Dad! What did you do?!" You shouted, running to Scott's body.
He was still breathing, fortunately.
"You need to leave," Melissa said (more like shouted). "Get out of this house!"
Scott was immediately rushed to the hospital, and he was going to be okay.
7 years later
Scott doesn't remember anything about that night. Stiles, Scott's best friend, showed up at the hospital and you told him what happened. Melissa made you guys promise to not tell Scott what happened. You hadn't seen your dad since then. It didn't matter. He was a drunk, and you didn't want him around.
