There may be a whole lot of headcanon in this, but just allow me to state that Namiko and Kichirou are not my original characters. I referenced the all-knowing Durarara wiki, where - lo and behold - I found those two names and no further information on them. I haven't read past the first light novel (saw the whole anime, of course), so... yeah, this is largely based on my own speculations. Of course, I did try to keep it loyal to the series, and it's in-character, I suppose, insofar as this is set prior to canon. Wish I owned it all, man - then I wouldn't need to worry about keeping with canon. (Please just consider that a disclaimer.)
Lastly. My intention was just cute brotherly fluff, really, but if you do ship Shizu/Kasu, feel free to squint and see that in this. :)
He wakes up late one night to the sound of his own name – muffled by shōji doors and the echoes of a feverish dream – but he's not being called. Rather, it's a conspiratorial murmur – it would have sounded hushed even had he been in the same room as the speaker.
"…Shizuo…"
He lies with eyes open wide to drink in the oppressive darkness of his bedroom. He's struggling to make out something more than muffled utterances throbbing through the distance, but he knows implicitly that what he'll hear isn't good. He recognizes the voices' owners and knows that his parents are worried, that he's been making them worry. He knows that late-night conversations can only mean secret concern and guilt and maybe blame, but that's why he listens.
It's why he climbs out from under the warm covers, steals toward the door and slides it back a centimeter at a time. He's still just a child, and underneath all the anger and the fear of his own strength he's just like any other kid. Any other normal kid, he tends to think, when he wishes the way he has so much lately that he were normal. He's drawn by the understandable need to know what his parents think about him – he's afraid, in a way, that he's at risk of losing their love. He might think that knowing will help him fix what's broken, and maybe he's just a little morbidly curious besides.
He inches down the hall, his bare feet creaking against the wooded floor as he presses himself into the wall. And the words gradually separate themselves into something that makes sense – "…said that everyone's talking about what happened at the bakery. What am I supposed to tell the neighbors?"
"You don't have to tell them anything. We just need to make sure that he understands."
"But, Kichirou… I just don't know what else I can do…"
She's crying. Shizuo can hear the telltale wavering in her voice, and he hates himself for it. He's tempted to detach himself from the wall and rush to her side, but he knows – he knows so much more than he should at his age – that that won't help anything. It'll only make things harder for his mother, and she's carrying enough on her shoulders as it is without the added weight of his own childish needs.
As if it's childish to need love, to seek reassurance and to want to be included in discussions that directly involve him.
But that's what he cautions himself as he sinks to the floor by the open doorway – yellow light spilling out into the dark hall – and wraps his arms around his knees. He can feel his resentment growing like a weed around him, and when it's not directed inward at himself, it swiftly turns on anyone who happens to upset his fragile temperament.
"I feel like I might be afraid of him," Namiko sobs suddenly, and Shizuo feels his breath catch in his throat. He bites his lower lip and squeezes his eyes shut as his muscles twist his hands into tight little fists. There are tears burning and stinging just behind his eyelids, but he fights them with everything he has. His parents continue their conversation in hushed voices, unheeded now by the young brunette.
"Nii-san?"
He glances up at the sound of this third voice, sees through a blur the silhouette of his little brother trailing a worn blanket at his side. "Kasuka," he breathes, and he casts about for something that will make this scene something different from what it so clearly is. The younger boy says nothing, though, and his expression barely changes as he steps toward Shizuo and makes himself comfortable huddled at his brother's side. "Go back to bed," Shizuo whispers pleadingly, but Kasuka only shakes his head. He's not listening to his older brother, Shizuo realizes, but to the words of their parents in the next room.
"He's our child," their father says placatingly, "and he's not the monster everyone says he is." Shizuo can feel Kasuka's eyes on him, then, so he closes his own again as if he means to hide.
"I know. I know, but… where did we go wrong? What if the same thing happens to Kasuka?"
What if it does? Would that be Shizuo's fault, too? He feels an extra shock of fear for his brother's sake at the thought; the sudden, insurmountable wave of emotion leaves him trembling.
"Nii-san," he hears Kasuka whisper, and there is a touch of alarm in his voice. "Nii-san."
"Kasuka will be fine, dear. He has a good future ahead of him."
But what will Shizuo's future be if he never learns control? Will it always be like this – feared by everyone around him, resented and regarded with absolute suspicion by all? Will he wind up in jail, or dead? His parents have already tried psychologists, counselors, everything, and no results. He can't do it, he doesn't believe that he can and he's almost stopped trying.
"Nii-san, come on," Kasuka whispers to him, and Shizuo realizes that his little brother is standing again, tugging gently on one of his tightly-fisted hands. "Let's go," he repeats.
Shizuo is too dazed by that point to do more than follow. Still, he doesn't expect to be led not back to bed, but into the bright light of the living room. Kasuka is as seemingly apathetic as ever, but Shizuo can almost feel some purpose in the way he moves closer to the adults with his older brother in tow.
Their parents turn after what seems a long moment, surprised by the sudden movement and the whisper of bare feet on hard floor. Shizuo stares down at that floor, tracing the little dark lines to avoid meeting their gaze. He feels like a burglar caught red-handed, and all he has left is to await his comeuppance.
"Shizuo," his mother whispers, her voiced hushed now with regret. There's no anger, but Shizuo remains wary. "I'm so sorry, sweetie, were you there the whole time…?"
Kasuka nods beside him, then says, "Nii-san isn't wrong. He's doing his best."
Their parents exchange a quick glance, and his mother kneels in front of her two sons. "Shizuo," she says gently, and her oldest hesitantly raises his head. "Are you okay?" It's clear that he isn't, but there's not much else for her to say right then. She can't very well tell him that everything he's just heard has no meaning, because he's not stupid. He knows.
He knows, so he mumbles, "I'm okay." It's the least he can do, isn't it, to make up for all the trouble he's caused – all the trouble he'll continue to cause?
He feels a slight pressure on his hand and realizes that Kasuka is squeezing it – a gesture of comfort, of solidarity. The younger boy nods, just barely enough that Shizuo can catch the motion, and Shizuo remembers what he once asked his brother – "Aren't you afraid of me, too?" – as well as the response he'd received. Maybe it's not all that significant, but to Shizuo it means someone who can stand to be around him, someone he can rely on when he has nothing else to turn to.
It means that maybe he, too, can be permitted to worry, to fear and to feel hopeless. He doesn't have to say it, after all, because his brother knows without those tools called words. He knows, and he's there to lend his brother a hand when he needs it, to act as a mediator between Shizuo and the world with which he is so often at odds.
"I'm okay," Shizuo repeats, and this time he means it.
One day, he resolves, he will repay every one of his brother's favors. He'll control his strength, forge a future for himself, and finally stop relying on that mediation.