Rewritten.

I have a change of heart as to where this story is going to go. Thus, I am re writing this chapter. Sorry for any confusion!
I hope you all enjoy this rewrite!

PS. To the guest who asked about whether or not it would be a story or collection of one-shots:

I considered making this into a series of one-shots. However I think it may be more interesting and fun to think about adventures/situations Yukio and Rin may encounter due to this change and incorporate it into the story! n_n

Chapter 2: Experiment

After a very relaxing, very peaceful soak in the tub, Yukio dressed himself in his pyjamas, and started walking back to the room he shared with his twin. The teen took long strides through the abandoned hallway wanting to arrive as soon as possible. He could almost feel his brother's body pressed up against his while they both curled up on a single mattress, the covers sheathing their bodies.

Yukio shook his head. Woah there. Can we just pretend that you're a normal bookworm, please. The teen reasoned with himself.

While he was lost in thought, his mind wandered to the question: How exactly did he plan on finding a cure for his brother? Of course he would have to experiment and research, but the last thing he wanted was to use his brother as a lab rat. He could test for possible causes of the transformation, and collect some blood samples from his twin to work with. Though, taking blood from his brother was never an easy thing as he absolutely despised needles. Plus, he would probably have to do this in secret. He wouldn't exactly approve of this, seeing as it appears that he doesn't know there's something wrong with him.

The exorcist sighed and slowly slid open the door, careful not to make a sound. As he entered the room he noted that his twin was no longer tied to the bed post, but was comfortably tucked into Yukio's bed. He face-palmed.

How the hell-

Yukio found his tie on the floor, basically shredded to pieces. He twitched. If he was going to use his teeth, why not just use it to unknot the knot, and then pull?Why did he have to gnaw at it until the threads unraveled, and the fabric ripped. He firmly pinched the bridge of his nose in annoyance. To top this all off, the nuisance was now occupying HIS bed. He stalked towards the lump in his sheets, the way his glasses shone white in the moon light gave him a sinister look. He wanted to strangle the demon with the remains of his tie.

"Nngh...No...You're stupid." His brother said in his sleep, drooling on Yukio's pillow. God dammit.

"...I know you are... but what am I..." His brother said again. What is he? Three!?

It was certain that by now Yukio wanted to drag Rin's slobbering, lazy ass out of his bed. He looked behind him at the demon's bed, which was a mess of sheets, Yukio's precious manga, and clothes.

"You're kidding me." Yukio mumbled darkly. Considering some possibilities of what he was going to do with this hopeless case. Y'know what. Maybe it would be better if Yukio just locked Rin up and used him as a lab rat. Maybe teach him some discipline while he was at it. The younger twin pulled off his glasses, and quietly placed them on the night stand. He wasn't going to stand here all night and curse his brother, nor was he going to sleep in another bed. He also considered picking Rin up and throwing him back into his own bed, but the possibility that he was going to wake up, and cause a ruckus made Yukio go against it.

Climbing into bed, he was embraced by the warm, welcoming, and comforting sheets. As he slid in, Rin's ears suddenly perked up and he stiffened. Yukio didn't notice this slight action, and proceeded to get comfortable before covering himself with the blanket. His back faced Rin, and closed his eyes to slowly drift off into the realm of sleep that he openly invited to take him. He felt something warm rub against his back, it willed him into the world of sleep even faster. That is, until he heard a soft murmur of his name.

"Yukio...Are you asleep?" Rin mumbled against his back.

Yukio simply replied with a hum.

Rin scooted closer to the teen, and wrapped his arms around his torso. Yukio heard small noises that sounded like whimpers coming from his twin. Just as he was about to open his mouth to ask the other what was wrong, he felt a long, furry appendage slip between his legs to wrap itself around one of them. He then felt the other's almost hot breath on his shoulder, before a soft pair of lips trailed up along the length of his neck. Upon reaching his ear, Rin whispered the teen's name hotly before nibbling on his lobe.

Yukio was frozen where he lay, Rin had never been this straight forward in ministrations before when coaxing Yukio into taking him. The young genius found it strangely uncomfortable. Of course he found it to be a huge turn on, but some how it felt as though this wasn't really his brother. It wasn't his brother who was doing this, it wasn't his brother who wanted this. As much as he'd want to believe this was his twin, his gut instinct told him otherwise.

"Who are you...?" Yukio forced out, struggling to turn around to face his brother.

"What do you mean "who are you"? That's rude." Rin appeared to mock in a voice slightly deeper than his usual.

As Yukio rolled over to face his brother, he thought he saw red flash in the eyes of his beloved twin who immediately pushed Yukio onto his back, and sat himself just above the taller teen's crotch. The younger teen stared wide-eyed at his brother when he felt something hot and hard poke at his abdomen. The teen on top grinned a toothy grin, which displayed his razor sharp teeth almost threateningly. He allowed his palms to explore Yukio's muscular body, running over from his abs to his chest, and stopping at his shoulders.

Yukio was in a daze, and all he could do was watch as his twin did as he pleased with his body. Rin leaned down until his face was only centimetres away from the bottoming teen's face before cupping it, and teasingly graze his lips with his own before giving them a rough lick. Loving Yukio's reaction that appeared to show an inner conflict within the boy, Rin began to grind down on his brother. Moaning out his name sensually as he did so. His deep blue irises burning with passion, and instinct.

Instinct. Yukio thought.

Could it be that his brother was in heat? Yukio pondered for a moment, and as he paid more attention to the teen in front of him he realised that he was probably right. Though it wasn't much different from when Rin was usually horny. Except he wasn't this aggressive in getting what he wanted. It felt like he was dealing with an animal right now. Rin was desperately grinding his hips down on Yukio's to ease his need as he continued to cry out, and grip Yukio's shirt.

The bottoming teen sighed, having come to a decision. He gripped the teen's hips and forced them down harder onto his own, while he moved his up in sync with the movements. Rin's tongue darted out of his mouth as he released a strangled moan. His back arched, and he threw his head back as Yukio continued to guide him along. "M-More! I w-want you! Y-YUKIO!" He screamed out into the darkness. Yukio couldn't believe he was getting off so much from a little friction. He moved his hands to Rin's ass, and gave each cheek a harsh squeeze. The other gasped, and flew forward, landing on the strong chest of his brother. He panted as Yukio carried on. He noticed his brother's face buried into his chest, his smaller hands held his shirt in a death grip. He noticed his ears were downcast, and his smooth tail shot upwards. As if he was moving on his own, Yukio craned his neck slightly to nip Rin's newly acquired ears.

Rin realsed something between a moan and a screech, and Yukio grinned sadistically. He then slowly moved a hand from the globes of Rin's ass to the base of his tail, and gently trailed up. Rin stiffened, and cried one last time before Yukio felt a growing wet patch through the exwire's pants. He immediately dozed off on Yukio's chest the moment he finished. Yukio twitched.

Inconsiderate. He thought to himself as he palmed his own hard-on. He rolled Rin over so that he was lying on his back, and got off the bed to fetch his dirtied twin a new pair of pants (and to will off his hard-on of course). Once returning with a fresh pair in his hands, he grumbled as he removed his brother's pants. He was back at square one; cursing his brother for being troublesome as he tugged off the other's pants, and wiping him clean. He slid on a fresh pair of pants for his twin, and reached for his phone on the nightstand. 5am.

Might as well just get up, and start working now. He sighed. At least he was able to learn something new about his twin's new delicate body. His tail was extremely sensitive. He wondered why he hadn't ever noticed it before. He smirked. On the bright side of things, he knew how to deal with his twin if he ever tried to pull a stunt like that again. He might even use his newly gathered information as a form of punishment for his twin if he were to ever act up.

Seating himself at his desk, Yukio took another peak at his sleeping twin. He looked like any other household pet; curled up in a ball, with the tail wrapped securely around him. This was definitely going to be a pain in the ass. But Yukio wouldn't say that he disliked it. Maybe having his twin like this for a while wouldn't be so bad. He'd be able to have a little fun with him. Maybe train him to be a good boy.

He laughed to himself for making such a creepy remark. His mind drifted off to what Mephisto had told him, the conversation replayed again in his mind. He felt as though Mephisto was up to something. Why was an unknown, high-level demon able to infiltrate the True-Cross barrier? Why has this demon, and its abilities never been heard of? Why his brother?

It wasn't a mystery why both mankind and demons alike were out to get his brother. It was no surprise that he may be ambushed either. It would definitely be no surprise if he was kidnapped... Well, maybe slightly surprising because he would put up a damn good fight. But in all seriousness, why turn his brother in a cat? A useless, household pet? A useless, horny, household pet at that. That is what was surprising. Was this some kind of prank? Deep in thought, Yukio gathered his papers, and began filing his report whilst thinking of suitable ways to test for cures for his twin. It frustrated him that there were so many gaps in theories he thought up. So much missing information, so little logic behind the attack. All he could thinking about was why and how. Nothing appeared legitimate.

Of course, he could launch an investigation, possibly find some evidence - he could talk to a few tamers for possible information on the demon. This way it may be easier to find out the demon's intention, as well as a cure for his twin.

Yukio worked continuously through the early hours of the morning, determined to be prepared, and one step a head on the problem before him.

Yeah. So, I guess I've managed to figure out where this is going to head now. For those who really liked my smut, do not fear! A relevant smut will come soon enough and hopefully it will be better and more detailed than the previous one...

I hope you still enjoyed the re write anyway, I'll be posting chapter 3 soon enough ^o^