More thoughts on adjutant-less captains from my morning dog-walk:
I wonder if the role of vice-captain came out of the transition from Yamamoto's original band of blood-thirsty murders into a formal military. A thing we all joke about is how Bleach takes its most insanely powerful characters and makes them spend all their time filling out paperwork, but how did we get from there to here? I mean, think about Zaraki. His ass is not filling out equipment requisitions. Yumichika does that. Imagine you're Yamamoto and you've got these powerful, batshit personalities, and you're trying to negotiate with this existing nobility (the people who bound the Soul King) in their shiny city. We'll make a military, you say. Let them in, they'll fight for you, they'll protect you. Okay, the nobles say, but they have to follow rules. They have to lead people.
Yamamoto likes order. He started a school. He envisioned a military, not just a gang of personalities. But he had to start somewhere. And I think the first generation of that is baby steps. It's hard enough keeping those goons from murdering everyone who looks at them funny. So instead of making them come to meetings and fill out forms, they each get assigned some nerd to do that for them. If they want to be in the Gotei and get paid and fed and treated with respect, they can't kill their adjutant. If they are on Gotei business, they have to have their adjutant with them. The idea of an adjutantless captain is something dangerous, a rejection of the social contract.
To be honest, from the very beginning, I have loved the translation choice of "adjutant" for vice-captain, because it's an administrative role. It's especially delicious because at the time we hear it, because it comes from Byakuya, the only captain we've met so far, and whatever we've seen Renji doing for him, "adjutant" doesn't seem like the right word for it.
But Byakuya doesn't exist in the mold of the original Gotei-13. He fits more of the real-world paradigm of the rich and noble being given leadership positions in the military and bringing their way of life with them. The Gotei seems to be moving in that direction over time, all too eager to paper over its rough origins.
I think calling Gin and Zaraki in particular "adjutantless captains" is a direct call-back to that earlier time. Byakuya is calling them uncivilized; two criminals from the Rukon who are running around without their handlers.
There's a worldbuilding detail that's brought up a couple of times that captains have a right to choose their adjutant, and I think that actually makes this even more interesting. On one hand, that could have been a later addition--after a few generations of captains, it's decided that they are now civilized enough that they can pick the person who answers their hell butterflies for them. Alternatively, it could have been part of that original compact, an acknowledgment that the OG captains will play nice, but they will not be lap dogs.
