I don't own durarara

Summary: Best friend sibling Au

If anyone were to ask Izaya how he and Kasuka became friends, well he would just say that his overly friendly personality caused everyone to love him; Kasuka being one of those people. But if anyone were to ask Kasuka how he and Izaya became friends, he would probably shrug before saying something like "he likes my brother".

Which in fact does not answer the question, but instead raises more of them.

Izaya admits that his budding relationship with Kasuka had started simply because he was curious of the other males older brother. But he wouldn't deny that he doesn't consider Kasuka to be just as interesting. Probably his stoic face—along with his slight indifference to Izaya's infatuation for his older brother—made him curious enough for the devious brunette to call him his "best friend".

It wasn't exactly like the other didn't mind at all—he still rejected Izaya constant self-invitation to his house— but he at least didn't mind when Izaya would pester him to talk about Shizuo. Not that the other revealed much; he was a man of little words.

So he wasn't exactly shocked that people found their friendship to be odd. It also wasn't odd that when Izaya did meet Shizuo, Kasuka was anything but happy.

But what was shocking to Izaya, was that when he and Shizuo got together. He found himself unwillingly wanting to reveal it to Kasuka. Not that Shizuo wanted to reveal their relationship to his precious little brother, but the blond did feel guilty enough that he was thinking of doing it. And the fact that Izaya was feeling just as guilty, made him uncomfortable.

He swore that his guilt was all Shizuo's fault; the brute made him soft. Yet, he knew that that wasn't fully true. As soft as Shizuo made him with all his emotions; he knew that most of his guilt came from becoming too close to Kasuka.

They might be an odd pair of friends, but Kasuka was one of the few people who he could not fool easily. Maybe that's why Shizuo and Kasuka were so—as much as he hated to admit it—important to him. It wasn't everyday that Izaya couldn't get away with manipulating someone with his words, and it was thrilling to have people in his life like that.

But even if they both did feel guilty, they somehow couldn't bring themselves to either tell Kasuka nor end their relationship.

It lasted only two months before either of them could take keeping their secret quiet any longer.

"We should tell Kasuka," Shizuo said as they laid down on Izaya's bed. Izaya couldn't help the frown that settled on his face at the prospect of telling his friend the truth. He was trying to postpone—since he would not admit that he was cowardly avoiding it— for as long as possible. It didn't help that the damn blond wouldn't drop the subject unless he silenced him with a kiss.

"Fine, you can tell him."

"We will tell him," the other demanded. He wants to whine and protest, but Shizuo doesn't allow him as much a squeak before he gets up and starts getting dressed.

"Right now?! Shizuo, I realize you are a bit slow, but you do know we just had sex and we are not exactly presentable. I mean I can't even walk properly right now."

He wouldn't lie that he still enjoyed insulting Shizuo from time to time, especially since he loved seeing the angry face he would make.

"You call me an idiot, but it seems you have forgotten they have these things called showers."

"Oh yes, i'm dating a real genius. What about the fact that I can't even stand for a long time since you couldn't hold back."

With a sigh Shizuo decided it would be best to end their little quarrel early, and instead went back to where Izaya was laying down on the bed to lift him up and take him to take a shower. It would be faster if they both went in together anyway.

Of course Shizuo should have realized, that as soon as he had the brunette in his arms, Izaya would do anything to distract him. The distraction being little nibbles on his neck and earlobe. Yeah, this wouldn't be any faster.

It took them about an hour or so until they finally made it to Shizuo's parents place. They wasted another few more minutes outside the door arguing about how they were going to break the news.

Luckily—or unluckily, seeing as both were still nervous— Kasuka opened the front door mid argument. Startled, they stiffen, looking at Kasuka as if he had just caught them doing something more suspicious than what they were actually doing.

"H-hi," Shizuo stuttered out, causing Izaya to snort at his horrible attempt to act casual. Instead of answering his brother, Kasuka just walked back to the living room where the t.v. was on. Probably had been watching his favorite television show and had been alerted of their quarrel since neither of them had thought of lowering their voice, especially not Shizuo.

"So… um.. there is something we need to tell you Kasuka," Shizuo said, as they all make their way to the couch.

Kasuka only nods as he pauses his show and gives them all his attention. And for once, Izaya finds himself unable to come up with anything to say. As always Kasuka has a blank stare, but Izaya swears the other was glaring at him. They all sit in silence in what feels like eternity, and he can feel Shizuo anxiously jiggle his leg.

The action only seems to put Izaya more on edge, and in the end he blurts out.

"I'm fucking your brother."

In retrospect, he probably could have formed a better way to say that. But with his emotions out of whack, and still unsure if he and Shizuo were anything but fuck buddies. He couldn't think of anything else.

Shizuo sputters angrily, unable to find anything eloquent to say, but was embarrassed nonetheless.

"I know," Kasuka eventually says. Calm and collected, he only shrugs when they both look at him in what he assumes to be shock.

"Izaya stopped pestering me to tell him about you, and you have been going out more often than not. So can I continue watching my show?"

Still in shock they both just nod, and the sound of the t.v. fills the empty noise.

Well that was anticlimactic, Izaya can't help to think before he starts laughing.

Tumblr ask. If you want to find me at tumblr, my url is Kagami-and-Shizuo :) (sorry if there are any grammatical mistakes, please tell me if you find any)