FULL SUMMARY: When Usagi Tsukino stumbles into Mamoru's apartment one night, he believes their meeting is just a mere coincidence, because, honestly, what would a Physics major have in common with an undergraduate studying Child Development? But, before he knows it, she's charmed him and has roped him into her life, dragging him to places, teaching him new things; even calling him by an affectionate nickname. He's not sure what that rumbling feeling in his stomach is, but he's got a clue that it's what the rest of the universe calls "love".

A/N:A friend of mine on Tumblr asked me to write a Usa/Mamo fic with the prompt "wtf you're not my roommate, how did you get in here? oh sHIT you're really drunk aND NOW YOU'RE CRYING OKay okay it's okay shhhh, you can stay here i guess?" AU. This will most likely progress into a multi-chapter? Who knows? We'll see (: Also feel free to let me know how this sounds - bad characterization, incorrect grammar, amazing plot - any feedback is greatly appreciated!

The loud screams of drunken undergraduates caused Mamoru Chiba to jump in his seat, surprised at the sound of the stomping feet down the hall. He turned towards his door, as if glaring at the sources would stop the other students from running around and give him some well-deserved peace. The past week had consisted of four exams, and, though Friday night had finally graced him with its presence, two of his professors had decided to randomly assign two new papers, both of which were due this upcoming week.

He was pretty angry right now.

And Kunzite, his roommate, the cheeky bastard, had decided to go to a fraternity party, in order to meet the theatrical blond with whom he had been flirting with for weeks. Mamoru briefly wished he had accepted his invitation to come along, as he was starting to want to drink away his worries, but any ounce of regret was immediately pushed away when he thought of how he'd be third-wheeling Kunzite and the "child of love".

Now, someone was banging on his door for the eleventh time that night, further angering Mamoru due to the fact that, because of these people, he had been stuck on the same opening paragraph of his first paper for two hours.

He headed over to the door, ready to swing it open and yell at the person behind it.

What he didn't expect was the door to open before he grasped the doorknob, and a petite blond to stumble into his arms. He yelped and fell backwards, causing his glasses to go askew. Rubbing the back of his head, he looked down at the short girl, who was giggling quietly with her face buried into his chest.

He ran a hand through his dark hair, his annoyance level now at a peak. "Excuse me-"

"Soooorry!" the girl giggled, rolling over onto her back, her two long ponytails sprawled across the floor, "I didn't expect you to be at the door."

"What-"

"Say, do you have any water?" the girl was now on her feet, blinking and scanning the room, "I'm very very thirsty for some water."

"Excuse me," Mamoru got up to his feet, adjusting his glasses, "Who are you and what are you doing? I opened the door to ask you to be more quiet."

"Oh don't be such a grouchy-butt," the stranger giggled, gently smacking him on the arm, "Loosen up a little butt- oops, bit!"

Mamoru rolled his eyes, "Hilarious. Now please, leave-"

"Do you have any water?"

"No, I don't. Please leave."

The girl pouted, crossing her arms, "You're lying."

Mamoru sighed, gesturing to his door, "Yes. Now please, leave. I have a lot of assignments to complete, and you're distracting me-"

"It's a Friday night!" the girl twirled around, her ponytails swishing around and almost knocking over his cup of tea, "C'mon, join the party!"

"Thank you for the offer, but I decline."

Her lower lip stuck out more, her blue eyes now squinting at Mamoru, and brought her hands up to her head, where her hair was rolled up into two buns atop the ponytails, "My magic hair tells me…...you're weird."

"I'm weird?" Mamoru demanded, realizing he was under scrutiny, "You're the one who stumbled into my room, without warning, obviously drunk-"

"Only a little bit drunk-"

"It doesn't matter! Now you won't leave when I ask you to, and you're constantly asking if I have water, and I really need to get to starting these papers, and-"

Sniffle.

Mamoru immediately ceased his yelling at the girl, who now had fat tears falling down her red cheeks.

'Shit, Chiba, what have you done?' he thought, now regretting his words.

"Listen, I'm sorry-"

"I-I'm sorry, I didn't know you'd get so mad!" the girl sniffled, wiping her tears, "I-I just came in using the key that Kunzite gave me, because h-he told me to bring h-him and Minako a condom, and-" she was now bawling loudly, and Mamoru suddenly felt like an ass.

"I-I'm sorry, erm, Miss, I've just been really stressed," Mamoru tried to console her, his hand stuck between reaching out to pat her on the back or keeping it to himself, "It was unfair to take it out on you, and….I'm sorry."

The girl's cries reduced back to sniffles, and she peered up at him with watery, light blue eyes, as if figuring out whether his apology was genuine.

"Um," Mamoru gulped, afraid she was going to start crying again, "I'm Mamoru, Kunzite's roommate."

Her lips stretched out into a small smile, and she wiped her eyes before extending her right arm out, "I'm Usagi, Minako's roommate."

"I'm assuming Minako's the theatrical blond Kunzite's been chasing after?"

"Yeah," she nodded, tears continuing to trickle down her face, "I'm sorry I bothered you, Kunzite didn't tell me you'd be here."

"It's not a big deal," Mamoru lied, knowing that his lack of process would bite him in the ass later, seeing as he had more to do this weekend. So much for his planned-out weekend schedule, "I overreacted, I'm just kinda tired of all these noises."

Usagi giggled, sniffling, "I-I should probably leave-"

"You could stay."

The words had left Mamoru's mouth before he could stop them.

'C'mon, Chiba. "You could stay"? You barely know her, and-'

"Really?" her eyes lit up with anticipation, "I-I mean, only if I can, but Minako and I's apartment is all the way in 40-C, and it's kinda dark, and-"

Mamoru found himself smiling, "Sure, you can take my bed, and I'll sleep on the sofa so you can be comfortable-"

"No, no!" Usagi shook her head quickly, grabbing Mamoru's arm, "You should sleep in your bed! I'm the guest, I'll sleep on the sofa!"

He ran a hand through his hair, "I don't think that guests are supposed to-"

"We could share the bed!"

Mamoru's face flushed a dark red, "W-What?!"

"I'm not a blanket hogger, I promise!" Usagi exclaimed, "But if you're worried about anything else, like sleepwalking, or-"

"You barely know me," Mamoru interjected, "We're undergraduate students in college who met five minutes ago, and you want to sleep in the same bed?"

"I may still be drunk," Usagi giggled, continuing to tug on his arm, "C'mooon, it won't be too bad."

"That's not a proper response," Mamoru said, now frowning.

Usagi stopped dragging him and pouted, "I trust you not to anything. You're too nerdy."

For some strange reason, he felt offended by that.

"Still- erm, miss-"

"Usagi," she reminded him, and he nodded.

"Right, Usagi- I really don't mind, I could sleep on the sofa, I-"

Suddenly his arm felt ten times lighter and he watched as the petite blond ran away from him, her short legs seeming to be headed towards the bathroom.

Oh.

He ran after her and flicked the light on only to see her hunched over the toilet, emptying the contents of her stomach into the wide bowl. Heading over, he crouched down and pulled her ponytails back with one hand, rubbing her back with the other.

"Thanks," Usagi mumbled, her good mood evidently gone, "I-I think I-" her words disappeared as she faced the toilet again and threw up.

As a pre-medical student, Mamoru knew he shouldn't have felt grossed out by the noise Usagi was making, but he couldn't help it.

After finally finishing her vomit session, Usagi shuddered quietly, slumping over the bowl. She looked up at Mamoru, a weak smile now on her face. "Sorry."

"It's no trouble," Mamoru said awkwardly, not sure how to comfort a random girl who had just thrown up in his bathroom, "Maybe you should lay down."

Nodding slowly, Usagi latched on to Mamoru's offered hand, allowing him to help her stand up and walk to his bedroom. He walked over to his bed and gestured for her to sit down. "I'll be back with some water."

After she nodded again, Mamoru left his room and headed towards the kitchen, pouring a glass of water for Usagi. How this quiet evening had turned into one of such craziness, he had no clue, but at least the sounds outside had quieted down.

Usagi was glancing around his room when he entered his room, a small grin on her face, "You have a medical terminology poster?" she asked.

"I am a pre-med student," Mamoru rolled his eyes, handing the water to her, "It never hurts to begin studying early in life."

"Nerd," she said softly as she brought the glass to her lips, "Thank you, though."

"For the water, or for letting you throw up in my apartment?"

Usagi giggled, smacking him gently, "Shut up."

"Or that you came into my apartment with the keys-"

"Shhhh!" Usagi was now laughing, setting the water down on his bedside drawer, "You're the one who should be sorry. Who wears that shirt," she gestured to his bright green pullover, with "EARTH" written on it in yellow print, "with those jeans?"

"Fine, fine, I didn't realize you were the fashion police."

"I mean, it looks like you're wearing a pajama top-"

"Okay, okay!" Mamoru exclaimed, "I get it, I don't have the best fashion taste."

"I mean, if it weren't for those glasses, you wouldn't look half as cute as you do now."

Mamoru felt his face heat up in embarrassment, and attempted to get up, trying to leave the awkward situation, "Alright, well, you're obviously still drunk, so erm-"

"Mamoru, stay here!" Usagi protested, grabbing his arm again, "I wasn't kidding when I said we should share the bed. Come oooooon. I'm sober enough to be saying this, trust me."

"I really should get back to working-"

"I'm not taking no for an answer!"

Mamoru sighed. 'Constantly be tugged on or lie down for a few minutes?'

"Alright…"

"Yay!" With a harsh force, she tugged him down onto the bed next to her, wrapping her arms around his shoulders, "Thank you."

Mamoru smiled slightly, but sighed again, running a hand through his hair.

What an evening.