I don't own Teen Wolf and never will. No copyright infringement intended.
The Derek that died in the fire reawakened the moment he saw Cora. He didn't realize it at the time, but something that broke inside of him repaired, at least a little. So, after he and Scott hunted down Boyd and Cora, they took the two teenagers back to his (no, their) old house.
Cora wasn't completely back to normal, but she shot a concerned glance at her older brother. "Please don't tell me you're living here."
He shook his head. "No, I have a loft, but this is the safest place right now." He didn't want Peter around Cora at all yet, if ever. And he wanted to make sure that Boyd was okay. Fuck, Erica was dead. Another death on his hands, and Derek wasn't sure how much more he could take. Why was he so wrong? No matter how much he tried to keep himself upright, he knew he was falling apart at the seams. This was his life and he had to live with his fuck ups for the entirety of it.
"Alright." Cora didn't feel completely normal yet, but she was definitely worried about Derek. Was this what he had been like without their family all this time? Once she got back on her feet, she was going to help him as much as she could.
"You okay there, Boyd?" Derek couldn't take his eyes off his little sister. He had gotten her killed, but here she was and now he was floundering. Well, he usually did since he fucked up so much, but now it was so much worse. Why hadn't he and Laura stuck around? Maybe they would have found her sooner and Cora wouldn't have been stuck with the Alphas. However, once she recovered, he was going to pry the full story out of her to see what happened.
Boyd nodded. "Okay for now. Erica's dead? I didn't imagine that?" He felt like his heart had been ripped out and he wasn't sure how to do this without her. He had been falling in love with her and now they could never see where their relationship was going to end up.
Derek closed his eyes for a few minutes to regain some composure before he spoke. "Yes, she is. I'm sorry." He didn't blame Boyd for wanting to leave now. Hell, he wouldn't be surprised if Cora decided to leave once she found out how he had killed their family. She'd probably blame him like Laura had. She always made sure to get in a little dig to remind him what he had done – Not that he needed to be reminded. But that was okay since he deserved it.
Cora noticed her brother getting lost in his own head and decided to put a stop to it. She staggered a little, but made her way over to Derek and hugged him. Surprised, he flinched, but after a few minutes of Cora not giving up, he reluctantly melted into it. Derek wanted to cry, but refused to let himself. Cora was the one who needed to cry. "Are you going to do this a lot, Cor?"
She laughed. "Maybe. I haven't seen you in a long time, big bro. I have a shitload to make up for."
"Language," he gently chided.
Cora rolled her eyes. "Come on, Derek. Anyway, I need to sleep so this is going to suck."
"I'll be right here if you need me." Derek doubted she would – Why would anyone need him? – But he wanted to make sure that she wasn't alone. He was never going to let her out of his sight again, no matter how irrational that was. He couldn't lose her again. He'd never be able to take that pain for a second time. He'd already lost too many people he loved and the losses just kept piling up. It was one of the main reasons he kept Peter around, despite needing his help with the Alphas. The overwhelming loneliness – no matter how much he deserved it – was too much to bear sometimes.
Cora just smiled at him. "I'll call you if I need anything. Promise. And wake me up if shit is going down. I may sleep through it, though, so whatever." She yawned and then lay down on the floor. She was asleep within minutes.
Derek stayed up all night to key an eye on Cora and Boyd. He absolutely refused to let the Alphas take them again and he was determined to do better this time (he doubted he even could. When had he ever done better?) so they'd look up to him (something else he doubted because they really shouldn't).
When Scott and Stiles stopped by the next morning, Derek was exhausted but Cora and Boyd were slowly recovering. The Alphas had done a number on them and it would take them a long time to heal, even with the accelerated healing. It was probably why Erica had died so quickly.
"It's nice to meet you." Stiles waved at Cora and she waved right back. They had known of each other, but hadn't been in the same classes together.
"So, we need a plan to take the Alphas down. I am not letting them get away with killing Erica and taking Boyd and Cora." They were going to pay for this; Derek would make sure of it.
"We'll help," Scott assured him, and Stiles nodded his head in agreement. He and Erica had just started to get along and he was hoping they could become friends. Now that was never going to happen and he was furious. Erica was just a teenager! She had her whole life ahead of her and now she'd never get to do anything she wanted to do. It was so fucking unfair he wanted to punch something (but not as hard as Derek because that shit was uncool).
"I don't want any of you to get hurt. That's why I kept you out of it In the first place." And Derek had someone to live for now with Cora back, but he wasn't about to mention that to them.
"Well, tough because we're in it now." Scott stared him down until Derek finally gave in and agreed to help him take the pack down.
Cora got up and hugged Derek again. "You better get used to this, Derek. I'm going to bug you so much."
"You always did." The old Derek was peeking out a little, which thrilled Cora, but it was obvious now that he wasn't ever going to be the brother she was used to.
Derek had broken completely after the fire and not even Cora would be able to bring his old self to the surface. But she helped, at least a little, and that went a long way. But life was never going to be the same again and Derek had to live with that.