A/N: This is really just an idea I got while decorating my own Christmas tree tonight, and I doubt it'll be anything more than a short oneshot. I might make a series of oneshots between them, but I'm much better at short drabbles like this than full-on plot fanfiction. Please let me know if you like it, and I'll consider writing more. Of course, ideas for other ones are appreciated as well. Oh, and sorry if anyone was offended by the Jesus comment, it's just Rei, y'know.

The lyrics included were from River by Robert Downey Jr.

"It's coming on Christmas,

They're cutting down trees,"

The grey-haired scientist swore he could hear the faint sound of music from what his roommate and occasional weapon had transformed into the homey living room of his laboratory. He turned the screw that protruded from his skull, focusing on the sound; it was, indeed, music, and Christmas music by the sound of it. Stein sighed, putting his hands in the pockets of his stitched up white lab coat as he left his office to go investigate.

"They're putting up reindeer,

And singing songs of joy and peace,"

Upon further inspection, aforementioned living room was completely covered in holiday decorations; tinsel and lights covered the walls, and in the corner of the room stood a large Christmas tree, probably around seven feet tall. Golden-white lights sparkled throughout the pine branches, dark red poinsettia leaves strategically placed across it. Before it stood Rei, his part-time weapon, wearing a traditional Santa hat, and placing a crystal bear ornament on one of the tree's branches. She hadn't yet noticed the professor's arrival, and was quietly humming along with the tune playing from her small radio across the room.

"You've certainly gotten into the Christmas spirit," Stein stated, sitting down on the couch across from the tree, dark green eyes watching her in amusement.

Her own blue eyes met his, turning back to smile at him. "Yeah. 'Tis the season, right?"

"I suppose it is," he replied, leaning back as he watched her pull more ornaments out of a nearly broken, old cardboard box, covered in rips, tape and pen marks. He found himself staring at the tree, unique decorations and all.

"Oh, I wish I had a river I could skate away on."

"What? Never had a Christmas tree before?" Rei asked, a joking tone to her voice as she noticed his eyes fixed on it.

"Not that I can remember," he answered bluntly, disregarding her sarcasm.

She only stared at him for several seconds, before setting down the ornament she had been holding and walking over to him. He glanced up at her questioningly, as she grabbed his hand. "Come on, you're helping me decorate it."

He blinked, silent for a moment before standing up and letting himself be led over by the shorter girl. "Why is it necessary to put decorations on a pine tree to celebrate the birthday of the possibly nonexistent son of God?"

"Who cares about Jesus? Christmas trees are charming," she answered with a grin, handing him an ornament.

"Oh, I wish I had a river so long,

I could teach my feet to fly,"

Within half an hour of decorating, sarcastic remarks and useless bickering, the battered box was empty and its contents were all hung on the tree. Well, except for one; with a glint of determination in her eyes, Rei reached in and pulled out a sparkling, red, star tree-topper. Turning back to face the challenge of the tree, she stood on her tip-toes and reached her arms up in an attempt to get it on the top. Stein stood back, a smirk tugging at his lips as he watched the short girl struggle with the star. Seeing her sigh in defeat as she stepped back, he grabbed the star from her hands and placed it atop the pine tree effortlessly, to Rei's disdain. He chuckled, amused at her annoyance as she crossed her arms across her chest in irritation.

"You could only reach it because you're abnormally tall," she stated.

"Perhaps you're abnormally short."

"I'm adorably short. It's not abnormal."

"Oh, I wish I had a river I could skate away on."

A short argument and the suggestion that breaking one's legs causes them to grow taller later, they stood back and admired the tree.

"I like it," Rei concluded, her signature grin returning to her face. Stein nodded in agreement, pulling a cigarette out of his coat pocket, balancing it between his lips, and lighting it. Normally, the weapon would've chastised him for ruining the fresh smell of the newly chopped down pine tree with the cigarette smoke, but her mind was occupied elsewhere as she skipped back over to the table on which the box was placed.

"One last thing," she started, the scientist turning to look over at her as she grabbed something previously tossed aside from the box. She picked it up and walked back over to Stein, smiling up at him. "Mistletoe~." She held up the mistletoe above them – or, rather, above herself, considering her height, but she tried – and kissed him on the cheek, fulfilling the Christmas tradition. "Merry Christmas," she finished, before turning to walk out of the living room and back upstairs to her own.

The grey-haired professor smiled ever so slightly, the rare kind that was filled with neither malicious intent nor insanity. He supposed the celebration of Christmas this year would be tolerable, now that he had someone to celebrate with.