Entry tags:
Thoughts on his brothers and such
He hates sharing the same face, always getting mistaken for his brothers but he also is grateful for them to be sextuplets. It's not every day that you get to say "I have five twin brothers!" so that alone is pretty cool, and because they were born at the same time and have that connection, they're closer than they would have been if they were born different years. And as much as he says "I wish I were an only child", Osomatsu is a person who needs others around him and would have ended up growing up way too lonely if he didn't have any siblings.
In the end, he loves his brothers and he's grateful to have been born with five best friends -- as shitty as they all can be. (Though he probably wishes they had a cute little sister for him to dote on, ngl. He'd eat that shit up.)

Karamatsu -- Out of all the twins, Karamatsu is the one who's always by Osomatsu's side -- literally and figuratively. Whenever they're lined up, it's just Karamatsu to his right or left and no one else on the other side so those two probably talk a lot behind the scenes just by convenience alone. And because he's the second eldest, those two have that older brother connection that they share, and Karamatsu steps up as the eldest in Oso's place when he can't be there or is acting irresponsible (ie. ep 24). I feel like if Osomatsu has any problems that he needs off his chest, he'd probably go to Karamatsu first but in absolute secret, because he'd get teased by the others for it. He wouldn't go for Karamatsu for any actual advice though, because his cheesy one liners aren't much help but Karamatsu probably listens really well so he uses him to vent his frustrations or worries, instead.
He realizes that Karamatsu is easily hurt and takes their teasing absolutely seriously and so he keeps it in mind not to tease him as much as the others do. Of course, he'll still ignore him completely when he says something cheesy, as they all do but he's seriously toned down the actual mocking since episode ten where Karamatsu asked for his advice about being less painful (I don't actually recall him being super mocky in the first place towards Kara though..). Also he secretly thinks Karamatsu's clothes are cool, so after a while he was probably like "man this is really hypocritical of me isn't it".

Choromatsu -- Since they were kids, Choromatsu had always been Osomatsu's partner in crime. But lately, he's been too focused on being responsible and adjusting to adult life that he hasn't wanted to get into any antics with Osomatsu anymore. Osomatsu wants to continue to have fun and goof off for however long he can manage, so the fact that Choromatsu is trying to move on is hard for him to deal with.
So that's why Osomatsu always edges Choromatsu on, and ignores Choro's remarks about him being childish or stupid, or not making any sense. Because if he can get Choromatsu to react to his stupid or nonsense situations, then he can keep him in the same childish mindset that Osomatsu, himself, is in. If there comes a day where Choromatsu responds to Oso's antics calmly, as if there isn't anything wrong with it or ignores him completely, then that would be the point where Osomatsu would give up, because it would mean that Choro has moved on completely.
It's also why, in the beginning of the Kamimatsu episode, Osomatsu randomly brought up the fact that he was tired of living with his brothers and told them to get jobs and move out already. It seemed kind of out of character of Osomatsu to bring that up, but in fact he was only doing it to see how serious Choromatsu was about it. He was absolutely delighted to see Choromatsu respond with "I'm not interested in getting a job at the slightest bit" -- he was relieved to see that Choro wasn't ready to grow up just yet. (It's also why Oso was strangely despondent and generally indifferent during the self-consciousness episode (except for when him and Totty were screaming at Choro for being annoying). That entire thing was Choro acting as if he was really going to graduate to adulthood this time so Osomatsu didn't really want anything to do with it.)

Ichimatsu -- The ever quiet and brooding Ichimatsu. Osomatsu's been, and probably always will be a little scared of Ichimatsu, because of his eerily silent but violently angry nature. He didn't tease or talk to Ichimatsu much at all in the early episodes, because he was genuinely scared that he'd do something to make Ichimatsu snap. He thinks Ichimatsu's a little weird with how quiet he is, because the rest of them are so loud and outgoing, but he also understands how hard it must be for him to come out of his shell so he doesn't try to push him out of it that much.
He's also come to the understanding that Ichimatsu is really lonely, and wants to make friends since ESP kitty, and that's changed his perspective of his brother a lot, actually. Since then, he's made an effort to talk to Ichimatsu more and he's not afraid to tease him as much anymore either, because teasing is his form of affection so he thinks that Ichimatsu's probably pretty happy whenever he teases him. He's also always, even when he was more scared of Ichimatsu thought he was pretty cute. He is part of the youngest bunch, after all, so he thinks all three of them are cute honestly.
He's also worried about Ichimatsu -- like genuinely worried for him because he knows he's going to have a harder time when they all eventually have to become independent. He's quiet and scary, and isn't good in stressful situations or under pressure so Osomatsu's scared that he won't be able to make it for himself in the future. If the day finally came where they absolutely had to become independent (not just them moving out on their own but like dire need to move out like if the house got sold or their parents died or lost their jobs or something), he'd probably offer to take Ichimatsu in with him out of all the others.

Jyushimatsu -- Jyushimatsu is kind of slowly taking Choro's place as Oso's partner in crime, I've noticed. They haven't had a whole lot of time shown together in the series, but they get into a lot of stupid shit when it's just the two of them because they're the "idiots" of the group, and also the two mood-makers/jokesters. Though naturally, all six of them are comedians but those two are the ones who just generally goof around the most, even during serious situations.
Osomatsu's probably a little mindful of Jyushimatsu, because his innocence and always smiling face is something Osomatsu would want to protect -- so he keeps an eye on his younger brother, especially when the going gets tough. He wouldn't worry if something serious happened like.. them all being forced to work/move out or kidnapped or some kind of physical threat because Jyushi is more than capable of taking care of himself in those situations, but when it comes to something emotionally devastating, he'd try his best to keep Jyushi's heart safe. (Ie. hiding his girlfriend's AV video from him...)
I think he'd be heartbroken if he ever saw Jyushimatsu stop acting like his goofy, weird self entirely and started taking things more seriously.

Todomatsu -- Osomatsu probably tries to dote on Totty because he's the youngest but it.. never works out well in the end. That being said, Totty is actually the most like Osomatsu -- the difference being he's more than willing to work to get somewhere and he uses sly tricks and guilting/playing innocent/being cute to get his way where Osomatsu is just.. extremely honest and blunt and shameless. But Oso has some respect for Totty's slyness because he uses it so well and gets his way so easily and that's something Oso wants to be able to do but just can't seem to pull it off well enough.
Though it's only impressive if it's not against himself, of course.
He's extremely bothered by the fact that Totty hides so much from them and seems to have a pretty well-off life -- he's probably worried that Totty's gonna be the first out of there (when Choro doesn't yknow. Get a job out of the blue from their dad.) so he really hates that Totty does this kind of stuff secretly. He probably has a small, nagging fear of waking up one day with Totty nowhere to be found, because he just up and moved somewhere without letting them know.
He's gotta be proud of him though, for being the most competent of them all despite being the youngest. If Totty decided one day to be independent, when Oso's mentally ready for it, he'll cheer him on. (Just don't do it in private Totty... please spare him that pain....)