Disclaimer: Adventure Time isn't mine!

Notes: Well, I've never written for Adventure Time before, but I've loved the show forever. Once Marshall and Fionna showed up, I knew that had to happen, even though I've never written anything for a fandom this huge. So, here it is! I don't know how many chapters it'll be, but we'll see what happens. Please please review!

His hand was cold in hers.

"I'm Marshall Lee," he said with a smug smile. "I remember you. The homeless one who now has a house due to my good graces. Filly? Fie?"

"Fionna the Human," she muttered, shaking and dropping his hand as quickly as possible.

"Ha. Human. As if I couldn't smell that a mile away," he smirked.

Fionna scowled, her fingers inching towards her sword. "What exactly is that supposed to mean, you treehouse-stealing tool face?"

It was not the best start to a friendship.

...

"You left your dumb socks behind my bed," Fionna said, a little more than a month later, standing at his door with one fist poised to knock and the other clutching some rather odorous footwear.

Marshall Lee frowned, leaning against the doorway. It was a bit of a sight, considering he was floating. That lumping boy was always floating. "When?"

"A hundred years ago or whatever! Whenever you last lived there. Take them!" To emphasize the statement she waved them around a little, and he coughed.

"How do you know they aren't yours?" he asked, retreating a few inches and gesturing for her to come in.

Perhaps she should have deliberated a little more before doing so, but deliberating was for dumb-butts, and Fionna was no dumb-butt. "Mine smell worse," she grumbled as she crossed the threshold.

Marshall laughed. It was a soft sound. "Fine, give 'em here."

She tossed them his way, and began absently picking at her fingertip as he unlaced his boots.

"What do you know," he said, slipping the crusty old socks on and wiggling his toes. "They fit." He paused, flipping upside down to admire the threadbare socks, his hair dangling. "I smell blood," he muttered all of a sudden, righting himself.

Fionna glanced up, and started to see Marshall instantly so close to her. His eyes were blacker than ink.

"You're hurt," he hissed, his fingers closing around her wrist.

"It's just a splinter," she said. "I got it from touching that stupid M you carved."

"You touched my M?" Marshall asked, raising his eyebrows.

Fionna blushed a tiny bit, then felt foolish for it and tried to jerk her hand back. "Well, it's my treehouse now, which makes it my M. I can touch it if I want!"

He laughed. "Whatever you say, Fi." Then he sighed, tilting her finger this way and that to examine the angry red spot pricked with a tiny piece of wood. "Poor baby human, this looks like it hurts."

"Look, screwy, I'm tough," Fionna snapped, trying to pull away again and failing. "You don't have to treat me like a kid!"

Marshall said nothing, seemingly ignoring her words, his dark eyebrows lowered as he examined the offending sliver of tree bark. "You think twelve is old?"

"I'm nearly thirteen–"

"Try being a thousand, Fionna," he said, yanking the splinter from her skin with two pinched fingernails. "There. All better."

"Math," Fionna said sharply, taking a breath and stepping away. "Thanks," she muttered after a moment.

He grinned. "Anytime."

"The blood doesn't bother you?" she wondered, examining the welling crimson drop on her fingertip.

He shrugged. "Not after a thousand years. Red is enough." He looked at his socks again, and then slowly floated down, like a particularly fluffy snowflake, only more punk. For the first time in decades, the Vampire King's feet touched the ground. He simply stood for a moment, and then with a squeal of glee he pushed off and went sliding across the polished floor on his socked feet.

She simply stared.

"Ah, Fionna, you've got to try this!" he called, whizzing past.

Not able to bear the thought of him having more fun than her, Fionna immediately stripped off her shoes and shoved off the wall. It felt like flying, soaring on the shiny, almost untouched wood, and after a second she threw her arms out and laughed.

"I used to do this all the time at the treehouse," Marshall said, flipping black hair from his eyes and elbowing the couch to keep up speed, "back when the floors were still new. Me and Ashlynn had the best time."

"Who's Ashlynn?" Fionna asked. Distracted, she didn't manage to stop in time, and crashed into a wall.

Marshall laughed, leaning down to help her up. "An old girlfriend. Scum-sucking psycho."

"What'd she do?"

"Mm. She sold something really important to me."

"Relationships are stupid," Fionna said, swinging around the corner and skimming down the hall. Marshall followed behind, and she could see from how his eyes gleamed he had no intention of letting her reach the end of the hallway first. "I'd rather be friends than date."

"Even with Gumball?" Marshall asked wickedly, slipping by and beating her to the end.

Fionna blushed, and Marshall smirked.

"I wish I could do that," he said.

"Do what?"

"Turn cute and pink like you can."

At that, Fionna's blush darkened, smearing across her cheeks and the bridge of her nose. "Gumball's pink all the time," she muttered, spinning and heading back to the living room. Silently she thought that the Candy Prince was cute all the time, too.

Marshall sneered a little, his fangs showing as he cocked his head at her.

"Pink is a manly color!" she said hotly, skidding to a halt at his front door.

Marshall rolled his eyes. "Whatever you say, Fi."

"Hey, wanna come over for dinner?" she asked, slipping her disproportionately tiny feet into her shoes.

He slid to a stop and reached for his boots. "Got anything red?"

"Spaghetti with red sauce! Can't go wrong, bro."

He looked at her. "Cake'll flip."

She shrugged, and Marshall grinned.

"I always loved it when her tail got poofy anyways," he said.