At first, Lucifer didn't pay much attention to Nick. Nick did what most souls did when their bodies were being used as an angel's vessel: he burrowed deep under Lucifer's grace, snuggled close, and went to sleep. It was sort of nice, a warm little soul pulsing steadily against him, nestled under his wings. The cold didn't seem to bother Nick at all. In fact, Lucifer suspected he liked it. Nick was with him for maybe a month, before Nick stirred, deep in the recesses of their shared brain. 'Luke?' Nick yawned.
'I'm here.' Lucifer hesitated, and then asked, 'Are you okay? Why are you up?'
'Not sure.'
Nick snuggled closer, clinging to Lucifer's grace, and Lucifer jumped in surprise when Nick buried his face in his feathers. 'Mmm. You cold?' Nick still sounded sleepy, content, and he so unbelievably warm. Nick tried to wrap his arms around Lucifer, nuzzling him, mumbling sweetly. 'Come on, come here, I'll keep you warm…' Lucifer consider shoving him away, telling him to stop or go back to sleep or something, but…ah, well. What was the harm? He sort of liked the little human, and it'd been so long since someone touched him. Lucifer relaxed a little and let Nick continue. 'I don't feel cold. I just am.'
'Do I feel warm to you?'
'You have no idea.'
His hand sought Nick out, scratching his back lightly, and got an appreciative noise as his reward. 'Can I stay awake? I don't want to sleep anymore.' Nick was still pressed tight to Lucifer's feathers, not realizing how…intimate that was. 'Whatever you want. Just don't try to take control back. You'll hurt yourself.'
'Okay.'

After that, Nick started talking to him, near constant commentary on the world around them. He also moved a lot, shifting around against Lucifer's grace, seeming determined to rub up against every inch of Lucifer. Lucifer would absently mindedly touch back, petting Nick's soul, cradling him tightly, pressing that delicious heat in close. Nick would sigh happily and nuzzle in, curled into a warm ball of energy. 'You're so cute.' Lucifer teased once.
'You like it.'
Nick countered. 'I keep you warm.'
'Such a sweetie.'
Lucifer crooned, wrapping his wings around his human, rocking him. 'I am so keeping you.'
'I'm not a stray cat.'
Nick murmured, even as he turned his head to kiss Lucifer's wings.
'Stray humans, stray cats, what's the difference to me?' Lucifer chuckled. 'Other than the fact that you're more fun to talk to.'
'A cat can't do this.' Nick went back to kissing Lucifer's wings, knowing how much he loved that. 'Mmm. Such a quick learner…' Someone was asking for Lucifer's attention, but he was busy. 'Don't go?' Nick asked, clinging to him.
'I'll be back, hold tight, okay?'
Lucifer snuggled Nick in close, and moved back to the frontal lobe. "Yes, Meg?" Nick was still being held in his wings, safe and cool and content. Right where he belonged.

"Nick? Sweetheart, come on, open up those pretty eyes." Nick blinked, groggy and sore and exhausted. Sam Winchester was smiling down at him. No. No—"Luke?" He croaked.
"Got it in one." Lucifer murmured, and kissed him. Nick moaned at the rush of grace surging through him, mending injuries, waking him up, cleaning his skin and clothes, and he felt familiar wings brush against him. "Thought I lost you for a second." Lucifer laughed nervously, trying not to let on how afraid he'd been. He sat up, pulling Nick into his lap. "Feels so good to really hold you." Nick tucked his head under Lucifer's chin. Those wings encased him, cradling him as always. "I can't wait to get you to a bed. Make love to you." Lucifer whispered, lips against Nick's hair. "Hell, I'd be willing to go at it right here. But, you deserve a little better." Nick mumbled in agreement, his face hidden in the crook of Lucifer's neck. Lucifer laughed suddenly, loud and gorgeous, and Nick fell madly in love with the sound. "Poor Nicky." He teased. "Still sleepy? Need a proper nap and a hot bath?"
"Please." He said, hugging Lucifer tightly.
"Anything you want, sweetheart." Lucifer shifted him away, kissed his welcoming lips again, and rubbed his back. "Come on, let's get you home."

"Luke." Nick whimpered. "Luke, please, ah, harder, want it, please!" He had his legs wrapped around Lucifer's hips, and his hands were tied to the headboard. He felt helpless and vulnerable and owned and desperately, deeply, endlessly loved. Lucifer growled, but didn't move faster or harder. "Don't want to hurt you. Shh, Nick, enjoy this, this is about you, making you feel good." Nick whimpered again, but closed his eyes and relaxed. "Love you." Lucifer whispered against his neck. "So much. So precious. Do anything to protect you."
"Ah, Luke, ah, ah, THERE!"
"Hmm? Here?"
"YES!" Lucifer kissed him into silence.
"Relax. Let me. I've got you." Nick clung to him all night, not caring that his hips were bruised, his chest hickeyed, and his muscles aching. "That was amazing." He sighed, and Lucifer dropped his wings down over them, invisible feathers tickling Nick's naked skin. "We can do that any time you want, any way you want." Lucifer promised, stroking his hair. "Now go to sleep, sweetheart. I'll be right here when you wake up."

Nick was a lot stronger than he looked, as Dean found out when the neurosurgeon's fist met his jaw just outside Stull cemetery. "Bring him back!" Nick screamed, and Dean actually took a step back, a little afraid. "I can't." Was the only answer he could come up with. That earned him another punch, and seriously, did Lucifer teach him kung-fu? The blond was gone before Dean could gather his wits enough to retaliate. Way, way, way down below, Lucifer was beating fruitlessly against the roof of the cage, his shouts fading to desperate sobs. He fell to his knees, not caring that Michael was shouting, or that Sam was staring, or that Adam was cowering in the corner. "Nick." He sobbed into his folded arms, curling up on the floor miserably. "Nicky, my Nicky, I'm sorry, I'm so sorry, didn't mean to leave you, don't do anything stupid, I'm sorry sweetheart, I'll come back to you, even if it kills me I'll come back to you." It was a long time before Michael came to comfort him, before Adam nervously hugged him tight and said, 'Calm down man I'm sure he's fine,' before Sam wormed his way into the group and murmured something that was trying to be an apology. Way, way, way, up above, Nick busted the window of the crumbling temple, and crawled inside. Local legend said in the (supposedly cursed) basement, there was a door. A very old, very special door, that none of the villagers liked to talk about too much. His back-pack was stuffed with ritual supplies, and if this didn't work, there were six other locations in South America he could try. He'd scower the world until he found it. No jungle was too dense, no mountain too cold, no desert too scorching, no temple too haunted, no corner of the world too far, too remote, too dangerous. He was going to get back to his angel or die trying.