This is based off of my own thoughts/predictions. I haven't read ANY spoilers, so I don't want to say spoiler warning since this is just speculation. This was inspired by my thoughts of how Killian was able to resist Rumple's commands for a little bit when Rumple had his heart, because of his love for Emma, so I thought it might be a nice parallel to explore.
Disclaimer: I do not own Once Upon a Time or its characters; I'm borrowing them for my own pleasure.
"Emma," Killian said, trying to through to the woman inside the darkness. She chose to ignore him, watching as the waves crashed against the docks. He sighed and decided to continue anyway. "Look, I think I know what you're doing. I've got it down to two options, and I think that in either case, you can't tell us." He saw her stiffen, but finally turn around to smirk at him.
"So you've got it all figured out, huh?" She snarked, a painful reminder of the darkness that'd taken root in her body.
"I don't know, but I know you can't tell me if I do," he said quietly, doing his best to keep her temper from flaring up before she'd had a chance to hear him out. From her carefully neutral face, he knew he was right. "Either Arthur got his hands on the dagger and commanded you to give into the darkness, or you're only pretending to be this 'dark'," he said, using air quotes.
"You think I'm pretending?" She hissed.
"Emma, none of us can remember a thing from Camelot. You're a smart lass; if you really have some evil plan, you'd have just continued looking like you used to and pretended everything was fine, that we saved you, while continuing with your plan with us none the wiser. So whatever it is you're doing, it's for the greater good. I believe that, because I believe in you, and I know you." He paused to hold her gaze and search it for any traces of his Emma. "Swan, you're bloody brilliant, and you're so, so strong. Stronger than you give yourself credit for, and I know you wouldn't have given up without one hell of a fight or a good reason. You could've hidden your basement from me, so we wouldn't find Excalibur. Yet you didn't, and I know that, at least deep down, you wanted me to find it. Indirectly showing me the basement door wouldn't have gone against any commands from Arthur. So whatever happened, I don't blame you for not being able to tell us."
He wasn't even entirely sure he was right about anything, but if he was even close at all, he wanted Emma to know that at least one person wasn't angry with her, if in fact this whole mess wasn't her fault.
He saw it in her eyes, for a brief second; they softened, as if she was finally able to get some of the weight off her shoulders, and he knew he was at least partially right. She reached her hand up to grasp his, shakily, as if she was fighting against some unseen force determined to keep it at her side.
And he just knew.
"I know, Love, I understand," he said, not sure if Arthur was able to listen in to every one of her interactions. It was the same thing he'd done to her, to get her to understand without tipping off Rumple. He pulled her in for a hug, overwhelmed by the need to make sure she was okay. He knew that beneath the veneer of the Dark One, his Emma was still in there, and he could feel that she was hurting. She was stiff at first, the darkness telling her not to accept his comfort, but she eventually decided to (just this once, she told herself) let him wrap his arms around her and hold her, like hold times. She pulled back, her eyes still soft, willing him to understand she didn't mean her next words, but had to say them out of necessity to keep Arthur from knowing Killian knew –or he would surely be killed.
"God, you're so easy to play," she sneered, her voice cold and emotionless. "You know nothing about me." With that, she poofed off again, much like she'd done on their fake date. For the first time in a while, Killian felt like there was hope again. He at least knew partially what was really going on, and he had confirmation that his Emma –his light in the darkness, his girlfriend, his tough lass– was most definitely in there, fighting to be freed from the dark cage trapping her.