There was no such thing as 'officially moving in' with them.

Natasha had been sleeping in Sherlock's bed for over three years. She had all of her clothes in his dresser drawers and in his wardrobe, came home to him after every mission, tucked her books into his shelves, and had weapons hidden all around his flat. Even her tattered copy of War and Peace had a permanent spot on his nightstand, right next to their phones, and the tartan dressing gown she'd stolen from him during the first full week she'd stayed over hung from a hook behind his bedroom door, just for her.

She was used to Sherlock's experiments in the kitchen, finding body parts in the freezer or in the tub or, once, by the window behind the kitchen sink. The organized chaos he preferred had taken some getting used to, as accustomed as she was to clean, spartan surroundings, but she loved it now. Coming home to Billy the Skull next to a vase of beautiful red roses, or finding a stack of correspondence impaled by a dagger she'd gifted Sherlock from a mission in Morocco, it made her heart flutter and stomach flip.

The place felt familiar and warm and theirs, and yes, maybe that was sentimental and silly and Sherlock would probably tease her if he knew, but she didn't care. Not after so many years of the two of them making such a comfortable home of their loneliness.

So, no, there was no such thing as officially moving in together when they'd been doing this for all these years now, but somewhere along the way, between Sherlock's cases and Natasha's missions, and all the nights spent dancing or playing the violin or cuddling Rosie on the couch, pressing each other against any available surface after going too long without each other's touch, they'd naturally started calling all of this 'home'.

On the eve of what would've been their four-year anniversary of moving in, Natasha sat on the bed after a long mission abroad, slathering rose scented lotion on her legs, wearing one of Sherlock's shirts and little else. They didn't keep count of the time they'd been living together, since it had happened so gradually it would've been difficult to pinpoint an exact date, but it had been around this time that he'd given her a key, officially, and the memory made her smile.

Sherlock had spent most of the day with Rosie, case-less for the moment, but it was just the two of them now. Natasha peeked at him where he'd stretched out beside her, bare-chested and on his side, with his arm tucked beneath his pillow. His curls were damp, his eyes half open, and he played with her hair, longer now than it had ever been.

His eyes flicked up to watch her face, and she felt herself flush.

"Still," he said, letting her hair go to brush the rosy apple of her cheek with his fingers. "After all this time."

"Can't help it, unfortunately." Natasha leaned in to steal a kiss and drew back to cap her lotion, dropping it back inside the bedside drawer. "Rosie doing okay?"

"Mm, we watched Princess Diaries one and two today," he answered informatively. Natasha laughed, leaning back against the headboard, and his lips tugged at the corner like he wanted to smile too. "Highly educational for both of us," he added. "Gave me an idea for an experiment."

"Oh?"

Sherlock sat up on the bed and Natasha watched in amusement as he reached behind to grab his pillow, bringing it forward and weighing it in his hands. He made a soft noise of satisfaction, peeked at her, and before she could ask, smacked her square in the chest.

There was a silent pause. "Okay," she said slowly, finally, dragging out the vowel. "Is the experiment how many hits you can get in before I choke you with my thighs? Because I can tell you right now, the answer's one."

His eyes dropped to her bare thighs, visible past the hem of her stolen shirt where they weren't covered by their navy blue bedsheets. "While my head between your thighs is usually an exceedingly attractive outcome, though mostly when there is no choking involved, of course, that was not the intended purpose of the experiment."

Natasha exhaled a light laugh. "Cheeky," she teased, and Sherlock's his lips tugged into that dimpled, bright-eyed smile of his that always made her swoon a little. "What was the intended purpose, then?"

"A pillow fight," he answered without preamble. "I thought that was obvious."

"Would've been, but then there was all that talk about your head between my thighs and I kind of lost track." She pushed herself up on her knees, grabbing her pillow as Sherlock rose up on the mattress. "You really want to do this, dorogoy?"

"Which one," he said, like the cheeky bastard he was. He lifted his pillow in front of his chest, tossed it once in the air, broke out in another smile and added, "Do both?"

Natasha winked, coiled and ready to pounce. "Deal."

She lunged and he dodged, swinging his pillow and missing her by a hair. Natasha swung back with a huff, aiming for his head. She let out a squeal when he tackled her to her back, tickling her ribs, and he stole a kiss, laughing against her lips. Later, after, when one of the pillows burst open at the seams and sent feathers flying into the air and over the bed and down to the floor, Natasha collapsed on her back in a fit of giggles with Sherlock's face pressed into her shoulder. She could feel his rumbly laugh vibrating against her side and it only made her giggle more, the way she only ever did with him, all light and happy and too smitten for words.

She tucked her free hand in his hair, turned her head to kiss his temple and burrowed closer. "Martha's going to kill you," she whispered in his ear.

"Worth it," he breathed back. "I won."

She huffed. "Did you, now?"

"That was your pillow that burst," he pointed out, pulling back to hover with his face just inches from hers, looking far too smug. "Does that not mean you forfeit? And if you do forfeit, does that not mean I win? I did look up the rules, but they weren't clear. Should write them myself, since no one else has apparently bothered."

Natasha stared up at him with a stupid smile on her face, biting on her lower lip. There were little white feathers in his hair, and she knew she must have so many feathers in her hair, too. But Sherlock had this look in his eyes like she was the most beautiful thing he'd ever seen, and she felt like she might just melt right into the mattress.

She let out a quiet laugh, reaching up to brush away some of the feathers. "I guess that does make sense," she conceded, and he hummed like it should've been obvious. "Can't say no to you when you look at me like that, anyway."

"No, you can't," he agreed, smiling down at her with his eyes all soft. "I happen to like that about you, Natalia."

Sherlock kissed the giggle from her lips, slow and sweet as he tangled his fingers in her hair, deep as he nudged her legs apart. She tugged him down, closer, and he settled between her thighs, drawing back only to kiss beneath her jaw, down her neck, popping buttons as he went, pushing her stolen shirt out of the way. Natasha bit her lip, propping herself up a bit as Sherlock looked up, smiling against her skin.

His hands slid over the curve of her hips and pulled her down. "Your turn now."