Somewhere in middle school is when they truly started to drift apart.
Osomatsu will always blame it on the teachers, who after years of them never being alone, always existing as a unit more than as separate kids, decided putting sextuplets in the same homeroom would simply be too much effort.
For a while, they walked to and from school together still, but then they met other people, people in their classes or after-school activities or cram school, and slowly, like ships on a sea that gradually grows wilder, waves crashing higher and higher, suddenly they're alone.
And it can be deceiving.
At home they can pretend it's fine. They will never stop being who they are, the Matsuno brothers, and entity more than individuals, and Osomatsu at the head of that, their leader who sees them through the storm.
Then he looks behind himself and they're gone.
He knows that's when it started too. The other stuff. The emptiness that couldn't really be overcome by anything except those things he shouldn't even consider.
It hurts.
But if they're happy that is the important part to him. Osomatsu doesn't care if every day of small talk with different faces makes him feel emptier and emptier and emptier on the inside. If he feels as if without them, there isn't anything that matters anymore.
They don't need him.
They all seem perfectly fine without him. Choromatsu has excellent grades now and Totty is popular and Jyushimatsu plays baseball after school. Ichimatsu is harder to read, but even he doesn't look like he's struggling.
Oh, and Karamatsu has drama club, of course.
They're all doing fine.
Osomatsu repeats that to himself, over and over, and he collects sharp things in his spare time for no particular reason. Just because he can. Or because holding them in his palm and squeezing, harder and tighter and closer, digging into the skin, makes him feel a bit less empty than before.
They don't need him. He might as well just disappear.
He's almost convinced of this, on the brink of giving in completely and maybe just, stopping, when things change again.
When he's walking home from school and he spots Karamatsu, not at drama club like he is supposed to be, but outside, fidgeting in place, apparently waiting for somebody.
Almost does Osomatsu just pass him by. It's none of his business who his brother hangs out with these days. He shouldn't care.
But something about the younger's demeanor. The shifting his weight from foot to foot. The nervous way he glances at the ground. Something about it sets off every single alarm bell Osomatsu owns in his near-empty head.
This isn't normal.
So he sticks around, casually fading into the background, and then there's some guy, clearly at least five years older than them and Karamatsu is talking to him, holding out his hand.
Something exchanges between them. Something Osomatsu doesn't need to see any closer to know what it is. He would recognize money from any distance after all.
Then the man is huffing, he seems angry, making violent gestures and Karamatsu is saying something Osomatsu can't quite catch, being too far away. Karamatsu lowers his face and drops his shoulders, shakes his head, and then it happens.
The man hits him.
It can't have been too hard of a punch, maybe more of a warning than anything, because Karamatsu stays upright, cradling his cheek suddenly with a wince, but it's more than Osomatsu needs.
In a blink of an eye, he's on the guy, catching him off guard and using that advantage to shove him over. The stranger grunts angrily as he hits the ground.
"Aniki?!" Karamatsu calls, surprised, but Osomatsu ignores him, placing himself between his brother and the man that just punched him, rifling through his pockets for something, anything, before this man gets up again to tower over them.
His fist curls around something cold and solid.
"You stay away from him, asshole," he hears himself say. It sounds like some kind of tacky line out of one of Choro's manga, which is more than a little embarrassing, but he's brandishing the pocket knife at the man without the slightest tremble in his hands, threatening.
"Whoa, whoa-" The guy in question holds his own hands up awkwardly now, trying to smile charmingly. Osomatsu recognizes him as one of the seniors he has seen around school. "We were just taking care of a little business transaction, no big deal."
"We don't want whatever you're selling," Osomatsu says coldly, glancing at Karamatsu but he is staring at the ground again, one eye already swelling up in blueish hues. "Just leave."
The senior doesn't need to be told twice.
Osomatsu turns around, barely remembering to lower the knife in his agitation. "Kara, are you insane? What were you doing?"
"It was fine," his brother says, regaining some of his bravado now and he grins sardonically. "I had everything under control."
"Like hell you did. What were you even- No, you know what? I don't need to know."
He sighs, flips the knife closed and Karamatsu follows it with his eyes.
"Since when do you carry that around?" he asks slowly.
"A while."
His brother scrutinizes him then and it's like he can see right through him. The only one who can. "Osomatsu, did you-"
"It's fine," he says mockingly, an echo of what his brother told him moments earlier. Maybe it's childish but if they're going to be keeping secrets from each other two can play that game.
Because they're thirteen years old and Karamatsu is buying pills from some kind of shady adult drug dealer after school. Because they're thirteen years old and Osomatsu carries around stolen knives he just as quickly would use on himself as on somebody else.
"Let's just go home and get you some ice," he says, throwing one arm around his brother's shoulder and Karamatsu nods, touching the side of his face gingerly.
Sometimes, Osomatsu thinks he might as well disappear. His brothers will be fine without him, it wouldn't matter a bit.
But then he knows at least one of them still needs him. So maybe he better stick around for now.