Hello, I've also posted this on a reddit page for Naruto but I really wonder about this.
and I am trying to figure out how this even happened. At first I mixed up Kumo with Kiri and hoped hidden mist Jutsu could obscure everything but apparently not. I know there might not be an actual answer, but I was hoping someone might have advice on what seems reasonable.
Right now I am thinking they just used lightning based enhancements to increase their speed, and it was more of a smash and grab operation. with fewer watchmen, and probably those that were on watch were injured or elderly, and perhaps a more celebratory (but within Hyuuga limits) atmosphere that let their guard down, they would have known but not been able to catch up?
maybe a Genjutsu? I am unclear on whether or not a Genjutsu is automatically broken by Byakugan. I know that trained users can break very powerful ones, but they also knew what they were looking for (Ao, why I assumed it was Kiri), and once again, elderly or not as well trained users that aren't expecting an attack.
Maybe they just have someone who can use hidden mist Jutsu, and that's part of what makes it so confusing to everyone. Obviously they are looking to add to their arsenal and I think it's a pretty underrated Jutsu. They use it, Konoha assumes Kiri is attacking or something. Byakugan is having trouble identifying chakra networks when there is chakra everywhere in the air.
If you have any ideas on these theories, or maybe a better one, I would appreciate it. I've searched but I don't think there is a clear answer. Anyways, any help would be appreciated.
Some people on reddit suggested that it was because the Hyuuga were sleeping. I just feel like that doesn't make sense for a clan like the Hyuuga, that all of them were alseep and had no night watch.
First of all: they are so worried about losing the Byakugan that they seal members of the branch family. The Uchiha don't do that, so we should assume they are more paranoid than other clans about their Dojutsu. You add to that that they are literally torturing people, and I think they are doing their best to keep it secluded and keep outsiders out. So I really don't think that they would just let their guard down completely at night, even if they were inside the village, because they act a little more paranoid than the Uchiha.
Second, this particular night has Kumo nin, who have already made previous attempts to gain the Byakugan, and who the entire country is currently at war with, visiting. "Peace Treaty" or no, I doubt that they just went to bed that night like everything was normal.
It has been shown all through the series that off-duty shinobi lower their guards within their own village. Even Tobirama was shown to stop using his sensory abilities in the village, even when having an important high level discussion with Hashirama. The only times we see the Hyuga with their Byakugan active within their compound is when they're training.
In regards to the night of the incident, Hiashi was pretty quick to react, so it's likely they were ready for such an attempt. We saw the diplomatic problems that resulted from him dealing with the intruder after he had taken his daughter, just imagine how much worse it would have been if he attacked before the Kumo-nin actually did anything.