I got curious about it and looked it up. Apparently, Kubo answers daily (?) questions of fans on Klub Outside: https://klub-outside.com/s/n136/?ima=2520
You can find a lot of them translated here: https://www.fanverse.org/threads/klub-outside-kubo-answers-translations.1239498/
To be honest, a lot of them sound like complete retcons he is trying to fake like it was something he had thought all along. But they all work very well, so who cares? Some I found interesting:
Q115:
Byakuya says that Ichigo is the second person to ever witness Senkei. Who was the first person to see it?
A115:
I cannot answer this here.
Q117:
Back when Old Man Zangetsu tried to tell his name to Ichigo inside his spiritual world, it was covered in black ink and couldn't be seen. Was that the doing of Ichibei Hyosube?
A117:
That is correct.
Q151:
I have a question regarding Yachiru Kusajishi. While she is Zaraki Kenpachi's Zanpakuto "Nozarashi", is her being called "Yachiru" the reason why she herself also possesses the Zanpakuto "Sanpo Kenju"?
Be it Hihio Zabimaru or Fuji Kujaku, there have been many scenes in which the Zanpakuto could not release their true power unless called by their true names. I am thinking that "Nozarashi" gained the essence of a Shinigami and took form due to being named after the real "Yachiru", name which also led to her obtaining the Sanpo Kenju sword which is specialized in the act of slashing.
I am really curious about the identity of Yachiru Kusajishi so it would be great if you could answer my question.
A151:
Oh, wow!
Despite there not even being a single passage written about Yachiru being Nozarashi, I'm amazed that you managed to find all that out!
As far as the content of your question are concerned, you are almost right.
In addition, Yachiru represents a form of Kenpachi's Bankai that was separated from its main body, and which gained the power of a Shinigami upon receiving a name from Kenpachi. The true embodiment of Nozarashi is that of a grown woman. Just imagine Zangetsu and Tensa Zangetsu, that should make it easier to understand.
Q213:
In regards to Byakuya's grandfather, Ginrei, when Kyoraku brought up the names of the Shinigami that have been Captains for over a hundred years he was not mentioned. Was his service as a Captain rather short?
A213:
I forgot about him! Let's blame it on Shunsui.
Q238:
When one inherits a Zanpakuto in the way Tosen and Kenpachi did, will the essence of its soul be overwritten? Or will it mix with the essence of the previous owner?
A238:
Usually it will be overwritten, but in some cases it can also mix.
Q308:
I personally find Ichigo to be the most handsome among all Jump series characters! Is there any Jump series protagonist that you find cool or handsome?
A308:
Usually, I don't really care much about the protagonists.
I do like Cygnus Hyoga though. I feel like I've mentioned this before...
(I quoted this one specifically because it has always looked to me like the Soul Society arc was totally rippe... based on the Gold Saints arc, so good confirmation that Kubo was a Saint Seiya reader)
Q346:
Is it possible for two Hollows to conceive an offspring?
A346:
Yes.
Q363:
We were introduced to a new Lieutenant in Atau Rindo, but what happened to former Lieutenant Iemura?
A363:
Since Atau's abilities were greater, he personally applied to be demoted to the position of 3rd Seat. Even though he was responsible for it, he fell into depression but thanks to Hanatarou's support he was summoned back into the 4th Division barracks and reinstated. The 4th Division is caught up in lots of paper work but this is what he's best at.
Q364:
I just read the new anniversary chapter. It's been so long since I last got this excited, I even got goosebumps!
Is this just a one shot or will there be a continuation? I wanna read the rest!!
A364:
I’m not really good at drawing something when I’m forced to. So I’ll consider doing it when people stop pestering me about it.
Q398:
Since Shawlong is the Arrancar designated as #11, would that make him the first Menos to have been turned into an Arrancar for Aizen? In that case, why did Aizen choose him as the first test subject?
A398:
That's because Shawlong himself advised Aizen to try it on him first.
Disappointed no one apparently asked about what happened at the ending of Grimmjow's flashback since that is probably the thing I want to know the most (but that's only because I really like Shawlong, a sentiment I doubt anyone shares).