In Chapters 96-97, Gyutaro Believes That Ume Was Of Such A Pure Spirit That She Was Easily Dyed By Her

In Chapters 96-97, Gyutaro believes that Ume was of such a pure spirit that she was easily dyed by her circumstances, she'd have been an entirely different, better person if only she had been born in a better place. Not only does he find it his fault that she became the way she was, but he believes that he'd still be Gyutaro--someone who would become a demon and loathe other people for their happiness--no matter how many times he's reborn. Gyutaro is probably the only one who believes this, though. Muzan was not surprised when Gyutaro was killed, he always figured he'd be a disappointment because there was still such a human side to him. Tanjiro found Gyutaro easily to see himself in, and Ume certainly did not care whether he was good or bad--he was always good to her.

When Ume was born, Gyutaro really tried to do better, but ultimately he still took the route of a horrible, loathsome person because there just was not much other recourse. He blames this on himself, being the root of his own evil, assumes he always had the heart of a demon. Gyutaro had things so bad that he could never even fathom his lot in life being better, much less that he might be better too. The way he defines himself in such black and white thinking, assuming the worst about himself at his core, is like how his conscience tries to make sense of things he feels guilt for. The fact that he does feel enough guilt to have to find self-hating excuses like this goes to show that, if born into a different life, he really would have the capacity to be a better person.

Yoriichi Type Zero has six arms because there was no other way to capture the movements Yoriichi was capable of.

Is this why Kokushibo has six eyes?

I've pointed it out before, but if that is the case, it adds even more irony to the "one" kanji in Kokushibo's eye (壱) being the same kanji used in Yoriichi's name.

kyojuro is not sleeping well these days

Honestly? My main piece of advice for writing well-rounded characters is to make them a little bit lame. No real living person is 100% cool and suave 100% of the time. Everyone's a little awkward sometimes, or gets too excited about something goofy, or has a silly fear, or laughs about stupid things. Being a bit of a loser is an incurable part of the human condition. Utilize that in your writing.