Assorted headcanons that also double as notes for me (it's long):
Between him and Naki, he’s the one who interacts with the rest of the toudan most when checking on their tasks, so more often than not, he’s the one who ends up listening to any complaints or settling arguments.
Sometimes, he can be strangely and suddenly blunt. Monoyoshi is, generally, a pretty honest and sincere guy, so this sudden bluntness is not typically out of maliciousness or lack of awareness, but the exact opposite. Sometimes you have to say what a person needs to hear VS what they want to, is how he thinks of it.
He’s the closest the honmaru has to a face since Naki is Naki and his saniwa is very determined not to show his unless necessary.
Although he’s not a good direct liar, Monoyoshi is not above omitting info if he deems it necessary (like tricking Houchou into actually doing his chores). Monoyoshi’s poker face isn’t the usual expectation of stoicism but rather his ability to be smiling and pleasant while keeping tabs of things in his brain.
Extremely good memory even by sword standards
Good with kids and babies!!! I will take this bit from the mihotose musical and inject it into my bloodstream. Whenever I think of a modern au I keep thinking of him as either an elementary teacher or aspiring to be one if high school/college au.
Less headcanon and more calling myself out: Sometimes I can’t decide if he’s just a happy go lucky ball of sunshine or a cheery dude with a granny’s soul so I’m so sorry if I seem to flip flop between both vibes.
Out of all the other Sadamune, Monoyoshi would probably find it the easiest to approach Kikkou first compared to the other two, then maybe Taikogane second, then Futasujihi.
He would feel the most unsure around Mikazuki and Norimune but still try to get along with them, and somewhat indifferent to Magoroku but tries not to let it show too much.
It’s unclear if he and Namazuo actually get along as friends or if they simply got used to each other after centuries of being together, which isn’t quite the same thing.
Actually enjoys clothes shopping quite a bit but the mun knows nothing about clothes on a technical level I'm so sorry my son
Struggles to fully live for himself, but he's learning to be a bit more selfish. He still tends to put aside he own wants/desires to please other people, especially his masters, but can stand his ground if he feels strongly enough against something. If left to himself, he can sometimes feel a bit lost.
His whole “silent, aloof” vibe can be so quickly and immediately crushed by his own hands. The moment a job is done this man is operating on whims and the occasional intrusive thought that wins.
Likes being depended on, especially by his saniwa (saying this in general not just Uchuu in specific). One wouldn’t expect it on first impression, but Nakigitsune does like taking care of people, but usually does so in the background. Without Ichigo though, this side of him has been drawn out to the forefront as the Toushirous certainly have noticed his efforts despite himself and now he’s been adopted into the uncle role.
Nakigitsune honestly wears his heart on his sleeve. He isn’t very emotive, but that doesn’t mean he still doesn’t feel strongly or have desires. He may struggle a little to turn something down (unless you’re Uchuu, then he has no problem in doing it at all), but he will never hide what he loves.
Yes, he likes fried tofu. I’ll get back to you on what specific dishes though.
Sudden touch affects him a bit more than most. Just the very idea of suddenly being hugged makes him uncomfortable, but…he can make an exception for the little ones and Ichigo.
Sometimes he will just casually follow Kogitsunemaru around when he’s bored. Kogi has gotten used to this.
(maybe) Crack HC: he has a horror gaming channel, but think more manlybadasshero in vibes/content, bro is scratching every corner of the internet for weird ass horror games to hyperfixate on. Every rare 1% of the time he speaks his comments loses their collective minds. Doesn't stream.
not crack: he does genuinely find horror media very fun tho, and probably has bought a gaming laptop with his own savings (that or Uchuu got it as a gift) alongside building up a movie and book collection.
Nakigitsune is the senior between them and the one dealing with Uchuu’s bullshit the longest. While they’re not Close, Nakigitsune is probably the closest Monoyoshi had to an older brother figure until his actual brothers showed up, and Monoyoshi was assigned to his squad after manifesting until he gained more experience. So Nakigitsune is still someone he respects a lot.
This actually makes Naki one of the few people he can more easily vent to, besides Sohaya.
They casually hang around each other sometimes during breaks as well.
Monoyoshi has gotten a headpat from Naki at least once and sometimes playfully offers his head to him.
This isn’t even a headcanon but him and Monoyoshi are so close in height oh my god;;;….Naki you are so fucking short;;;;. King….
Uchuu is not very fond of cats or cat-like swords and yet it’s the cat-like swords or swords with cats he’s most curious about. Nansen’s curse, the way Gokotai’s history manifested his tigers…it’s all too fascinating but his flight or fight can’t calm the fuck down around them long enough to get anything useful.
He also used to be uncomfortable around Naki’s fox as well. He’s gotten used to them over time, thanks to actually being able to communicate with them and the fox rarely leaving Naki’s side anyway.
His puppets are more like visual measures to his growth. How many he can keep functioning at once, how long they can even move independently without his direction or a specific purpose— these are improving over time with practice.
Uchuu’s obsession is also fueled a bit by a lingering regret— he could barely speak yet when his owner died, and couldn't even give her a proper burial, so he spent quite a bit of time with her body in a then silent house. When Uchuu had first brought something to life, it was out of that loneliness, but I feel like he would’ve attempted to do the same to Granny’s body soon afterwards. Thankfully it wouldn’t have worked, but it was one of the first steps in his obsession with refining his abilities and, in a sense, deconstructing life. To what end, he is extremely tight lipped about.
There are two libraries in the honmaru— one for public use that also doubles as a hangout spot for the swords, and a private collection behind Uchuu’s personal quarters. Only Monoyoshi, Nankaitarou, and Nakigitsune are allowed inside.
Despite all that, he wouldn’t actually intentionally do anything to harm his swords (though he was a little pushier and apathetic to them when first starting out, seeing his duties more as a punishment with a silver lining, but he chills out over time). Him and Nankaitarou get along rather well for obvious reasons, even if their focuses are a bit different, but he still gets something useful out of Teach’s research.
*Uchuu rattling the bars of his cage* HOW ARE THEY CREATING THESE AMALGAMATIONS. HOW???
So while Uchuu doesn't like people being in his business, one) he's a hypocrite, and two) he doesn't actually mind his swords visiting other saniwa or even going out into the modern world (within limits, mainly government based bc honestly he wouldn't actually care enough as long as they don't get in trouble with the law). It's just visitors he doesn't care for.
The intention behind him is that he’s supposed to be kind of shady, but more so when you don’t know much about him or even his face. Once you do, he’s still shady, but he’s also annoying as hell and. A mouse.
All the mouse dolls have small differences in their painted marks to help him tell them apart.
Fun fact: he’s based on a tandemaus design I made a few years ago. He was divorced in that universe.