"Cas?" Dean looked up from the woman he had killed only moments earlier. She couldn't have been much younger than him if not his age "Can I ask you a huge favor?" Dean looked at Cas with hurt in his eyes for what he had done, then back at the woman. She looked so peaceful and harmless. Dean hated himself for doing this. All she wanted was to find her parents and save Sam. Dean was disgusted at himself by how familiar that sounded.
Her motives are to find her mom and dad and help anyone in the process. His motives were to find his dad and kill every evil son-of-a-bitch they find on the way, saving lies in the process. Dean sickened himself.
"Dean, I can't." Cas looked at Dean to try and figure out his motives.
"What?" Dean looked angry, "Why the hell not!"
"I was sent from heaven with orders to kill her!" Cas said in a stern, deep voice, "Are you asking me to disobey my direct orders?"
"Why not? It's not like you haven't before."
Cas saw the sadness under the forced anger in Deans voice. He didn't like to see Dean this way: so upset but eager to hide it. It'll end up hurting him some day. Cas sighed, "One hour," Cas proposed, "If I still do not agree then I will kill her Dean."
"Yeah," Dean nodded his head, "Thanks Cas."
The angel walked over to Rose, the woman who lay dead on the floor in a puddle of her own blood. Cas looked over to Dean desperately hoping Dean would change his mind, but he didn't so the angel continued. He crouched over the woman, upset that he knew no matter what she said to him he would have to kill her, and touched her forehead.
"She's healed now. You should probably tie her up before she wakes up. Maybe something a little stronger this time," Cas looked towards the rope that looked too thick for even Sam and Dean to get out of, "I have a few angel and demon proofing symbols that may help keep her restrained this time. Sam you may want to put her in the panic room just in case we have anymore unexpected visitors."
"Alright," Dean said following Sam as he picked up Rose, letting her head rest against his chest.
Dean stopped, letting is younger brother walk down the stairs alone with Rose cradled in Sam's arms like a sleeping child, "Cas, this means a lot to me. Thanks for giving her a chance." Dean gave his angelic friend a genuine half smile but his eyes still remained sad and broken, "I asked for too much and I really appreciate your help, man."
With that Dean went to the basement and left Cas alone feeling his own betrayal towards his best friend, "I'm sorry Dean," he whispered so quiet he couldn't even hear it himself, "I'm so sorry."