I'm not quite used to creating humor/light-hearted fanfictions, being more of a angst/drama writer myself. And I know I will butcher the characters during this piece so I am just going to go ahead and warn you all that this may be a little (if not more) out of character. This is an idea that my beta and I were throwing around during our last month in the semester, and I remember her once challenging me to write something that wasn't slash. Womp. But I adore Lily and Marshall from HIMYM so I should have fun with this! I hope you all enjoy!

Disclaimer: I do not own the characters of How I Met Your Mother.

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"You know, when you asked me to come over and 'help you study,' I had something a little different in mind."

"Oh yeah? And what exactly did you have in mind?" Lily asked as she emerged from searching through her bag, quickly blowing a wayward strand of raven hair out of her face. Her boyfriend shrugged innocently, and then cast a not-so innocent look toward the bed at the opposite end of the room. Lily smiled in exhilaration and huffed out a chortle, tucking back her hair and continuing her rummaging. "That's Esther's bed."

"You hate Esther."

Lily smirked openly as she pulled out the roll of brushes from the bottom of her bag. Marshall wasn't lying. Ever since Lily had introduced herself to her roommate earlier that year, she was convinced that Esther Bauer was out to get her. Maybe it was her wild, frizzy hair that always managed to sneak over to Lily's side of the room, curling into a disgusting mass of brown tumbleweeds. Maybe it was her habit of eating the entirety of Lily's Apple Jacks every single time she went out and bought some. Or maybe it was how Esther wholeheartedly believed that her and Lily were the best of friends, acting borderline psychotic and terrifying the absolute shit of out Lily, causing her to firmly believe that one day she'd wake up to Esther's wide toothy grin as she held up a steak knife to slowly fillet Lily's skin off piece by piece.

Okay, well maybe not. But still, that girl was insane.

"True," she replied. "But I'd rather your reward for helping me out would be performed in my bed and not that of a serial killer."

Marshall scoffed in disbelief. "C'mon, she's weird, but she doesn't strike me as the serial killer type."

"Yesterday, she nearly sliced my arm open because she wanted to become blood sisters."

Marshall flinched, his eye twitching. "Okay, maybe she is the serial killer type."

Lily humphed in agreement and shifted on her bed as she sprawled her materials around her mattress. Putting Esther at the back of her mind, she sighed happily and scanned her supplies. "Okay, I have everything. Pants off, Erikson."

Marshall slyly grinned and leapt off the desk he was sitting on, hands working on unclasping his belt buckle.

"Down boy," Lily said, her brow raised in scorn. "This is for anatomy only."

"And what better way to study anatomy... than to show you mine?"

"Marshall."

Marshall gave out a whining groan, halting the process of removing his pants and throwing his head back. "Why do I have to do this again?"

"Cause I have to pass this stupid muscle practical, that's why," Lily answered, rolling her eyes at the prospect of her biology course ruining her life. "And to help me study..." She grinned, picking up a paintbrush and pointing it at her boyfriend. "... You're going to let me paint your leg muscles."

Marshall huffed but unbuckled his belt, dropping his tan khakis to his ankles and revealing gray boxer briefs. Lily giggled as Marshall stumbled slightly stepping out of the leg holes.

"My leg muscles better have a passing grade!" Marshall exclaimed, playfully flexing and clenching his calf muscles. "They'd better give you a freaking A!"

"If I do this right, they will," Lily assured.

She beckoned her boyfriend to sit in the designated chair in front of her. Marshall obliged, slumping down and raising the leg that was to be painted onto Lily's towel-covered thighs. Lily smiled, moving her paint pallet closer, and took a look at her canvas. She paused.

"... Did you shave your legs?"

Marshall clicked his tongue and rolled his head in exasperation, though his cheeks tinged pink in embarrassment. "If I hadn't, it would have- it would have been harder for you to paint and for me to wash!"

Lily raised her brows.

"Plus, I like the way it feels," Marshall eventually admitted, crossing his arms indignantly and looking away from his girlfriend's clear amusement.

"Okaaaay, let's start," Lily said, still smirking. She dipped her paint into her red paint. "And just an FYI, there will be no sex until after the practical. I mean it, no distractions. No kissing, no shenanigans of any sort. Just studying."

She barely painted on a mediocre version of the soleus and gastrocnemius muscles before she completely lost it, unable to cope with the constant flexing and contracting of Marshall's muscles beneath her hand, rippling until the ministrations of her paintbrush. She lunged at Marshall and hungrily crashed her mouth against his with a wanton moan. It effectively ruined any of the work she had accomplished, smearing the red and white paint all over her own skin and the bed sheets. The rest of the paint on the palette also joined the fray, spilling all over the mattress and coating the two naked bodies of Lily and Marshall.

Long story short, that was how Lily's obsession with Marshall's calf muscles began.