Being written for the Skyrim Kink Meme (but it's not showing up on the site for some reason…so I'll post here and send a link back to the OP if it doesn't show itself)
Prompt was: I really, REALLY want a Female!DB and Vilkas to be completely and honestly hateful with each other, but then they realize that behind that hate was actually pure honest love.
As the actual storyline in the game goes, Vilkas is kind of rude from the beginning... so let's say they just CANNOT STAND EACH OTHER. They are SO hateful, and SO rude to one another that Farkas and his love interest (either guy or girl, I don't care) decide to do something about it.
On a mission (fake or real), they take the Dragonborn and Vilkas and tie them together from the hands, not being able to come apart until they figure out a way to get along. Then of course after some time, maybe two-three days together, they realize they have feelings for each other.
Make it happen realistically! XD
* I would LOVE for a young DB (maybe a 18 to 20 year old Imperial blond girl)
* I want a very respectful Vilkas, as in, he has never slept with anyone before because he never thought of marrying any lovely lady he's encountered on his life.
* Sexyness after the problem has been resolved is also a plus, but not necessary.

TL;DR ~
F!DB and Vilkas hate each other so much but after Farkas and his LI tie them together, they mutually realize they actually hold honest romantic feelings and decide to act on them.

JUST GIVE ME WHAT YOU GOT.
I've never really written Vilkas before (except for a few lines he had in "Wedding Jitters") so I hope everything is in order.

"That was a cheap shot," Ruccia growled, wiping a trickle of blood from her lips. Vilkas scowled, towering over the young Imperial with his sword poised for the final blow. They were both covered in sweat and bruises, their "training" session having lasted from sunrise to well into the afternoon. The companion would have liked nothing better than to call it a day and go enjoy a mead or two with his brother, but the Imperial brat just wouldn't give up!

"Your enemies aren't going to fight fair," he lectured, sheathing his blade at his waist. "Now, accept your defeat. I never mind giving you a good thrashing but I'm tired of this little game." Vilkas turned on his heel and started for Jorrvaskr, leaving the girl to scramble to her feet.

"Don't walk away from me!"

Vilkas ignored her, shaking his head with a frown. He didn't join the companions to babysit snot-nosed kids who were barely off their mother's breast, and yet that's all he seemed to be doing lately! He would have a word—many, quite colorful words, in fact—with his Harbinger about the situation.

Ruccia shook her head, watching the man's steel-plated back retreat. She wasn't finished with him, not by a long shot. Not until she could pin that arrogant son-of-a-bitch and rub his nose in it like the disrespectful mutt he was! She was tired of being treated like a child (true, she hadn't yet reached her 18th summer yet, but it was only a few days away!) and blowing a strand of honey-blonde hair out of her amethyst eyes, she lunged at the older man.

Vilkas heard her coming and side-stepped her easily, but Ruccia wasn't so quickly deterred. She whirled around and decked him in the jaw, smirking triumphantly when he stumbled back with a pained grunt.

His steel-colored eyes landed on her and he growled. He tossed his shield and sword to the side and slipped the gauntlets off his hands. "I can see you have more than just 'friendly' training on your mind," he said, his voice dangerously calm, "Fine." Vilkas swung at the Imperial, their sparring turning into a full-fledged brawl in the courtyard. She may have been a woman, but she was (as much as Vilkas loathed to admit it) also a companion. If she wanted to be treated like an equal, then he'd show her what it was like.

He pulled no punches, not giving her a moment to breathe or retaliate in his assault. She blocked and strafed, trying to find an opening but he refused to give her one. All the while, he pummeled the Imperial with a scowl. Vilkas had never liked fighting women, it didn't make him feel like a man. But, by Ysmir, this woman drained every ounce of sanity he had and led him to do things he never in a thousand eras would have thought to do before.

Up at the Skyforge, Farkas leaned over the fence with a frown. He watched his brother and shield-sister go after each other's blood and shook his head. This wasn't what the companions were about! Ruccia was still new so he couldn't hold it against her, but his brother knew better.

"Should I go stop them?" He wondered, watching Ruccia knee Vilkas in the genitals with a wince. Soft arms snaked around his bicep and Farkas looked down at his wife, who watched the scuffle with her soft, topaz eyes. The sunlight danced in her cornsilk tresses, which were neatly braided down her back, and her pale skin was slightly sunburned from working in the forge all morning.

"Their fight is not yours, husband," She sighed with a shake of her head. "Ruccia is still young, and Vilkas has the temper of a small child, they need to settle this as children do."

"But Anjya," he started to protest. Anjya raised a hand to quiet him.

"If you interfere, it will only fuel their animosity. Let them get their anger out, then, they'll go inside and avoid each other for the rest of the day, as they always do."

Farkas watched them for a few more moments with a solemn sigh, "You're right."

Anjya smiled and kissed her husband's jaw, running her hand along his scruffy cheek as he smiled meekly and kissed her palm. His wife reminded him of Vilkas sometimes, always having the answer to any situation. But, unlike his brother, she was patient and understanding. He supposed that's what made her such a good Harbinger. Like Kodlak.

"Come," Anjya sighed, lacing her delicate fingers with his, "let's make sure Tilma has some medical supplies ready for when our siblings are finished with each other." Farkas nodded and followed his wife down the hill to Jorrvskr, casting one more look at the couple in the courtyard. They were on their backs now, fatigued and gasping for breath.

Ruccia felt around for a rock and weakly hurled it at Vilkas. "I hope a dragon eats you up and shits you out," she growled.

"Well, I hope a giant knocks you half-way to Elsweyr," Vilkas countered.

"I hope you get raped by a group of lonely Hagravens!"

"You are the most disturbing woman I've ever met!"

"At least I don't look like a woman!"

Vilkas smirked. Ruccia paused, then flushed.

"That's not what I…I meant that you…" She groaned in irritation, slamming her cracked and bloody fist onto the ground. "Just die, why don't you?"