She was laughing. Lucifer didn't find the situation humorous - from her end, particularly - so the gesture surprised him. He tilted his head to the side, curious eyes boring into her, almost as though he were able to read through every part of the soul that he was about to snatch away from her. "They won't hate you," Lucifer assured her calmly. "It's me that they will despise. You're being selfless. I'm the one dragging you under. I may be the one ending the world, but even I understand that."
Yes, she had to kiss him. It was a very unfortunate side effect of the deal procedures. Lucifer probably would have done away with it altogether, if not for the fact that his demons held it to their hearts dearly and would likely find it inconvenient if he changed the approach. While Lucifer didn't mind inconveniencing his demons per say, he didn't want to ruffle too many of their feathers as of yet. They still had a lot of work to do and Lucifer needed them at his right hand to do it. Not that he couldn't do it on his own, because he could. Lucifer was the one who had spread the Croatoan virus, he was the one who controlled the Horsmen, he was the one with the master plan and unlimited resources of power. The demons were simply useful. Tools, overall. Lucifer could have done away with them altogether, but he found their help more convenient. He could sit back, relax, and watch the people of the world burn at times, which Lucifer often found comforting in a sick sort of way.
"It's the only way," Lucifer confirmed. He didn't need to talk the girl into it, which he was grateful for. Lucifer was having a hard enough time getting himself prepared for the kiss. He didn't need for this twisted, shell of a human turned vampire to force him to pretend that kissing her was of importance to him.
When Caroline finally moved forward and tilted her head up to kiss him, Lucifer bowed his head down to meet her lips, the body of his vessel being much taller than that of Caroline's. The kiss wasn't enjoyable - not to him - so he made it as quick as possible. Unfortunately, there was only but so much one could do to make a soul pass through quickly when you were kissing someone. He had to hold it for a moment, allowing the feel of her soul to pass through him, thus sealing the deal that Caroline had been oh so very desperate to make.
Once that was finished, he pulled back. It took every bit of his willpower to keep himself from dragging a white sleeve across his mouth in disgust. "It's done," Lucifer said, turning away from her. "Your soul is mine now. As a vampire, you will have your uses. I'm going to need you to work with people you won't enjoy being around. I'm going to need you to kill people that you may not want to harm." Lucifer looked back at her, that sympathy wiped clean from his face. "But you're mine, Caroline. And you will do as I say."