青の祓魔師© 加藤 和恵; Beta-ed by AlixNight
It was like knocking into walls. There was no moving forward and no going back either.

Puberty, Rin decided, sucked.

Not only did his voice have to do down by at least two octaves, his body had to start producing those fucking hormones were constantly attempting to push him over the edge.

Damn testosterone. Rin's mouth pulled into a scowl when he found himself staring at something he wasn't supposed to.

Hastily and almost instinctively, Rin chewed on what was left of his pencil stub and glanced sideways at Yukio - once again. The brunet had his brows furrowed in intense concentration as he tapped his ball point pen for the eighth time against the top of the mahogany table, unintentionally creating a melody to go along to the mood.

Coming back to his senses, Rin quickly returned his attention to the thick set of papers right in front of his eyes. Mathematics had never been one of his better subjects (not that he actually received a passing grade for more than five times in his ten years of studying life), but calculus? Seriously? Rin failed to understand a single piece of shit that the teacher was teaching today, let alone comprehend it long enough to do this sixteen pages worth of questions.

Differentiate 2sin3x. That, was the question he was stuck at. Rin was certain that the teacher went through something that vaguely resembled this question in class today, but he was unable to retain enough information from class to solve this simple question. Sighing in defeat, Rin rummaged through his school bag and pulled out a detailed formula page which their teacher had joyfully proclaimed was filled with every single formula in the world.

Except the one he needed.

Rin crushed the sheet of paper and scored a goal when he tossed it directly into the bin placed at the far corner of the room. Glaring back down at the mathematics homework, the older twin fought an extreme urge to tear the offensive worksheet into shreds. Moreover, what was with this damn question? 2sin3x. Were two people supposed to sin three times or something?

Noticing how lame the previous statement in his mind sounded, the teenager growled lightly under his breath as he closed the booklet and prepared to chuck it into a corner so it would stay there until the rest of eternity was over. Or at least until he was feeling up enough for another round of one-on-one with those deadly math problems.

"Nii-san. Did you complete that assignment properly before you put it aside?"

Yukio attempted to sound annoyed while he chided Rin for his irresponsible behavior and demeanor. However, the sweat droplets rolling down the side of Yukio's face made it seem like he was nervous, rather than mad.

The brunet had a bottle of mineral water in his hands and looked like he had been gulping the cool liquid down his throat just moments before which was hardly surprising, considering the high outdoor temperatures.

"Nah. I hate math. And I don't like doing things that I hate." Rin retorted, a little harsher than he intended to - because heck, the summer heat was getting to him - and pulled off his navy blue shirt, before tossing the wad of cloth nonchalantly in the general direction of the laundry basket.

Yukio flinched a little, both eyes narrowing slightly behind his glasses while his features were flushed with a healthy shade of red. "You have this bad habit to complain a lot when you are upset."

The corners of Rin's mouth pulled up into a playful and lightly teasing smirk. "Annoyed?"

Yukio pushed his glasses up the bridge of his nose as he scowled darkly at Rin. His elder brother had what other people would call a sadistic streak, Yukio was certain of at least that much.

Rin sighed inwardly at his younger twin brother's silence and opened another packet of Popsicles, licking at the tip of the frozen blue treat. Yukio huffed furiously and tapped his feet against the wooden floorboards while he moved his feet in order to hear the soft creaking noises produced better. "I am."

"Need me to calm you down?" It was a joke. Really. Or maybe a joke with a deeper meaning, but anything beyond that would be stretching it a little. Besides, it was not like Yukio comprehend anything he was attempting to put across - the guy was a tad bit too innocent and took things too seriously for his own good.

Whoever ever said that twins were alike must definitely add to his statement that this only applied to identical twins, but not fraternal twins. At all.

"No thank you. But I can help you with your work if you ask me to, Nii-san." Yukio replied curtly, his tone a little taunting as he cast a deadly glare at Rin. "I don't need you to have another detention tomorrow afternoon and end up being late for another one of my classes. Plus, tomorrow is an important lesson for people like you who are aiming for the title of 'Knight'."

As if Rin needed any reminders to tell him that Yukio was his not only his little brother (who was now apparently taller and stronger than himself), but also his teacher and an exorcist of a much higher rank. Talk about a messed up world.

No matter how Rin tried to look at this, it was suppose to be the other way round.

The older twin shifted uncomfortably in his chair and reached over to grab a tissue to wipe off the blue stain on the desk, making sure to clean off all the traces before Yukio caught sight of it and went into another long lecture regarding food in their dormitory room. God bless the stupid summer heat.

Bless his idiotic hormones too. Rin crossed his legs and creased his brows in frustration. He hated, hated how close Yukio was to him right now because their arms would be touching if he would allow himself to lean an inch more to his left. Not that he would do that, ever.

They were family, god dammit, and Rin was certain that he definitely didn't want to go into an incestuous relationship anytime soon – provided that Yukio would actually agree to it in the very first place, which Rin was almost two hundred percent sure would never happen.

"When you differentiate 2sin3x, you get 6cos3x. Get that into your head already, Nii-san. Even if you completely forgot what we learned half a year ago, the least you can do is to recall what the teacher revised with us just yesterday."

The problem was that he couldn't do that. In class, he was always more interested in watching how Yukio's pen would move while he took notes and how the brunet would tuck his bangs behind his ear if he felt that they got in the way. Of course, no one ever caught him doing that because Yukio was conveniently seated in front of him so no matter how much Rin stared, it would seem as if he was just paying attention to the lessons only.

But he never did. "Then, what if I differentiate 6cos3x?"

"Then you will get -18sin3x." Yukio's script was elegant in comparison to Rin's own ugly scrawl. "And if you integrate the numbers you get after you differentiate them, you will get back the exact numbers before you differentiate. Do you understand?"

Rin hesitated for a vague moment before nodding his head numbly.

"Nii-san, can't you just admit that you don't understand what I just said? It makes explaining easier if you would just inform me about whatever you don't comprehend so I can come up with a better and simpler explanation!"

Rin narrowed his eyes and his left fist connected with the table top and the resulting thump sound resounded around the small dormitory room the two twin brothers shared. "Goddammit, I get what you said just now, Yukio! Exactly how stupid do you think I am?"

Grumbling furiously under his breath, Rin wrote his answer on the blanks provided and scratched the side of his head using the back of the pencil. He didn't exactly understand how the answer was supposedly derived but hey, it was the answer that Yukio supplied him with! There was no possible way that the answer the valedictorian came up with could be wrong.

Yukio pushed his glasses up the bridge of his nose while his tone took on a more authoritative edge. "Very, obviously. Next, can you do the first question of the assignment and then raise any queries you have left to ask me about."

Almost instantly, Rin raised his right hand up to signal that he had a question to raise. "Then tell me, Yukio. What do you think of incest?"

The bottle in Yukio's hands dropped straight down, the bottle cap clattering harshly against the ground as the mineral water flowed out onto the carpet and seeping into it, leaving a huge damp stain.

Rin grimaced – Pause. Stop. Rewind. Redo. Retake.

What did he just say? Rin glanced up warily at his younger twin brother and the utterly shocked expression on his face proved to Rin that there was definitely no taking back of his words. Oh, God.

"Nii-san, we grew up in a church. We should know better than anyone that such intimate relationship between two closely related family members isn't accepted in society, or any religious teachings for that matter." Yukio's tone was firm and his mouth set into a thin grim line as if to emphasize his point. "Incest is very-"

"Whoa, relax!" Rin exclaimed, putting both of his hands on both sides of Yukio's shoulders and pushed the taller teenager down into his seat before Yukio could even think of reaching for anything. "I just asked it because I saw that term in a book and yeah, I was curious. No big deal, don't read too much into it!"

Yukio gently released Rin's grip from his shoulders and leaned back into his chair so he could see the silly thousand watt smile his elder brother was wearing. "Are you sure you don't mean something else?"

Rin's smile disappeared without a trace. "Of course not!" He held out three fingers in front of Yukio's face and started folding them one after another as he started counting. "Reason number one, you are my family. Reason number two, incest is against the law. Reason number three, uh... Haha."

Unfortunately, Yukio didn't look the slightest bit amused.

"Reason number three, I'm your teacher-in-charge and it is against the school rules for teachers to date their students. It's written in the school handbook page 361, line 15, point number 3. You really should memorize the school handbook whenever you have the chance. That's the only way to make sure that you don't ever break a rule on accident – and frankly speaking 486 pages worth of rules is not a lot to memorize. Besides, I can always supervise you if you ask for it, Nii-san."

Rin blanched as he pondered how much of a demon his younger brother could possibly be.

A challenge from Sakura-fai.

A/N: It's been quite a long while since I post any fanfiction containing Yukio/Rin. Firstly, this was somehow tedious to write. I don't know why. Guess I've got to fit a fanfiction writing time slot into my schedule instead of frantically typing everything off the top of my head whenever I get the chance. Secondly, I want to thank my beta again, for helping me to proof-read this piece of work. Thirdly, I hope that this is good enough to fit the challenge. Lastly, this time, Rin is the one who likes Yukio. Really, I still don't get the reason why Yukio is always the one in love with Rin. Really.

Thank you everyone for taking the time to read this chapter, and please review.