Just a silly little thing. Probably around early to mid SuperS. For V, who loves established relationship fluff.

Mamoru knew for a fact that Usagi was capable of knocking properly. He'd seen it with his own eyes when they'd visited people together, plus she'd knocked on his own door a few times with normal, polite tapping - but never under good circumstances. He vividly remembered one time he opened the door unguarded - only to be startled by the very subject of his tortured thoughts smiling sheepishly before him, asking for help making curry rice of all things.

But, in any case, he didn't like thinking of that point in their relationship.

So, considering the alternative, he didn't mind her signature way to announce her arrival. "Mamo-chaaaan! I'm heeeerrreeee!" while pounding cheerfully on the door. "Mamo-chan!"

The only issue was, every moment he didn't answer, the louder her voice and pounding knocks became. She never got agitated or angry, just - louder. As if she assumed he must have found a place in the 700 square feet of his thin-walled apartment where for some reason he couldn't hear her. Out of consideration for the neighbors, he's have to drop what he was doing and scramble to answer, leaving pans on the stove or a book open on the table, phone conversations cut short, before anyone could complain about the bellowing MAMO-CHAAAANNNNNN echoing down the hall. Or, worse, before Usagi gave up and left - leaving his afternoon tragically lacking a certain odango'ed presence.

Once, she came by earlier than expected (especially by Usagi standards) and he was in the shower, having just applied shampoo, when her voice filtered through the running water. Cursing under his breath, he managed to make it to the door, towel slung around his waist and soapy water dripping into his eyes, just as she was inhaling in preparation for another yell.

She blinked.

"Well, come in," he said, with only slight irritation. Usagi nodded and scrambled inside, closing the door behind her before anyone came down the hallway.

"You answer the door like that?" she squeaked toward his departing back, her face turning crimson. He pushed wet bangs out of his face and blinked away the burning soap.

"I knew it was you," he threw over his shoulder, as he returned to the bathroom. "Make yourself at home."

After he emerged from the bathroom - fully dressed this time - he was greeted with the sight of Usagi laying back on the couch, legs slung over the armrest. She had headphones over her ears and was singing along to a pop song Mamoru guessed wasn't as off-key as she was making it seem, her pencil tapping against her cheek in time to the music. Her math book was propped up against her thighs but nestled inside it was an open manga, upon which she was deeply concentrating. A smattering of crumbs and an empty box of Pocky was strewn over his coffee table.

It was that exact moment he decided.

Mamoru honestly didn't think it was that big of a deal. But the way Usagi reacted when he absentmindedly tossed the key into her hands, it was like he was giving her the Hope diamond. "Oh yeah, I'd been meaning to give you this. Here you go. Don't lose it."

"What - what is it?" She asked, lifting the key up and looking at it like it might unlock the secret mysterious of space and time. Granted, the last new key she'd seen had done exactly that.

He raised an eyebrow. "I know you've seen one before. It works like this: you use it to unlock doors. I can show you how later if you want."

She gave him a withering look, that one he couldn't ever not smirk at, ever since he met her. "Mamo-chan," she huffed, her voice a warning.

"It's so you can let yourself in whenever you want," he shrugged, returning to his book. "And I can finish showers and what not without interruption."

Usagi blinked at him blankly for a moment before her brows knit. "It's...," she looked back and forth between the key and the door as if it would confirm for her, "for here?"

He glanced at her from the corner of his eye, "Yeah," he said, in a tone that made it clear he thought it was obvious. The dawning look on her face made him realize he better drop the book - and fast - in preparation of a full-on Tsukino Usagi tackle hug.

"MAMO-CHAN REALLY?!"

He managed to twist his body just in time to keep her head from crashing into the side table lamp, and settled her onto his lap with expert reflexes, even as she tightened her arms around him so tightly it almost hurt. For someone who despised physical activity, she was a lot stronger than she seemed sometimes.

"OH MY GOD, I CAN'T BELIEVE IT!" She kissed him so suddenly and quickly he didn't even have time to respond before she scrambled up and ran to the door.

"Does it really work?" She jumped into her shoes and skittered across the alcove to open the door and insert her key into the outside knob, twisting it back and forth. "Okay lock me out, see if it works!"

"Usako-"

"Oh, right, I'll do it!" The door slammed, and the few seconds of almost oppressive silence in her absence were broken with the click of the lock and deadbolt, and Usagi danced inside like she'd discovered the cure for ice cream headaches. "It works!"

"Yeah, I know," he said, "I tested it already."

But she was already settling in next to him again, pulling her knees to her chest and looking at the key in her palm fondly in silence for a very long time, while Mamoru returned to his book.

Finally, she turned to him, chin to his shoulder. "When can I use it?"

Again he gave her a teasing look. "When you want to enter the apartment, Usako." She let out a little frustrated bounce and groan that was way cuter than he'd ever admit.

"I mean, when am I not gonna bother you?"

"You don't bother me."

"Mamo-chaaaaan." Clearly that was not an acceptable answer. "C'mooon. I'm being serious."

"So am I." He didn't look up from his book, but his eyes had stopped scanning the page. "You don't bother me, Usako. Come over any time."

Little hands tugged on his wrist until he closed the book and turned to her disgruntled little face. It was hard not to laugh.

"What if you have people over?"

This time he did laugh a little. "Because you know me, always entertaining." Her pout was deepening from cute to dangerous and he dropped the teasing tone. "I usually don't have anyone over unless its Chibi-Usa or the girls," he pointed out, "with you along."

"What if you are studying?"

"Then you'll have to study too," he said, amused at how she wrinkled her nose in response.

"What if you are napping?"

"Then you can come in without waking me," he said, "so it works out."

"Okay, but what if you aren't home?"

"In that case, try not to eat all the food in the fridge."

Usagi opened her mouth, and closed it again. She was clearly trying to wrap her mind around something big, Mamoru just didn't know what it could be.

"But what if...," she shifted up onto her knees, bringing herself up to Mamoru's level. "What if it's really late at night and you are already asleep and I wake you up? Or, even if I didn't wake you up and you found me the next morning curled up next to you?!"

"I don't know where you got the idea that's something I'd dislike."

Shocked into silence, her cheeks flamed red before Mamoru quickly added, "But you shouldn't go out that late without a reason," he said, changing the direction of the conversation, "and in that case, I'd be there with you anyway."

Usagi nodded, "Good point." The hand not holding the key was nervously fidgeting. Her fingers twisted through the ends of her pigtails, blonde strands sliding through them in a way that Mamoru was trying very hard not to find hypnotic.

"But there must be some time you don't want me here," she said.

"If there was ever a reason, I'd tell you," he said, with an easy shrug. There was a pause, and he reached out and closed his hand over hers, stilling her finger combing. "What's wrong, Usako?"

"You...you really are okay with me... just coming over?" She wasn't looking at him as she continued, "You realize you are giving me unlimited access to your home, to your... life and-"

"You do know you have that already, right? It'll just be easier on the neighbors' eardrums now."

Usagi didn't take her eyes off their hands, entwined in her lap. She heard him place the book on the end table, felt him shift to more fully face her. "Usako?"

She still refused to look up, until he hooked a finger underneath her chin and gently lifted her face.

"Are you sure?" she said, finally, eyes shining with happiness.

"Yes," he confirmed. And then, well, she really was so close, and he couldn't see the harm in sealing it with a kiss.

"Hmmm..Mamo-chan-" she murmured.

"Yes?"

She leaned back a little, looking at him with a flirtatious sparkle in her eye that he still wasn't quite used to. "This means no more answering the door in a towel, doesn't it?"

"I'm afraid so."

She sighed, shook her head with exaggerated wistfulness. "Too bad. It was a good look for you."

"Get back to studying, Usako," he said, biting back a smile and picking up his book.

Instead, she went back to holding the key in her palms and looking at it steadily, her head leaning onto his shoulder a little smile playing across her lips.