Dump combat, gain Underwater Basketweaving Domain.
With Isan gone, Hazō is the last heir to its legacy.
Underwater Basketweaving x Primordial Sealing unlocks Underwater Basket Sealing. You can now produce seals with the weft and warp of wicker threads, and
bring with you whatever they make by putting it inside the basket.
"Willingness to eventually eat the faces of the primordial horrors that created you."
Willingness to face the fact that you'll eventually turn yourself into a horror and try to eat your loved ones' faces
The second we prove Primordial Sealing is Real and Useful, we're never getting deployed on a combat mission again, for sure.
Gives us more social time!
Oh boy we're going to have
so many meetings 
This is a 'rational' quest. The most rational explanation is that Hazo hallucinated out of desperation. Uh oh.
I understand "rational" as in "we patched the plot holes and made things make sense, people aren't completely ignorant or stupid and you're going to have to do some thinking to play," as opposed to "rationalist" which would be the twist of that: "what do I know, how do I know it, do I have to update my belief system" - think HPMOR. An entire plot hook and plotline about inner thought interpretation would toe the line, for all that the players are responsible as well. Also, not sure the QMs would enjoy that very much, though I can't speak for them.
At the very least, Hazō came out of this with new and then externally-verified knowledge (observation of Frog Kata), knowledge he did not expect (a different biome), and knowledge that actually surprised him (Jiraiya losing memories), with nothing overtly self-contradictory which he (or we) could pick apart. While a hallucination is not out of the question, it's not super likely in a context of a world with several cases of previously-observed spirit projection
and targeted resurrection, IMO.
??? Hazō has literally said, onscreen, "I don't know if this was real or not."
Oh so when Mari dismisses what Hazō says it's fine but when
we do it-- (jk)
We've seen the afterlife, we know it's a physical place where people who have died can move around and do things like that.
At the most technical, we've seen a place where Daizen went in the middle of a seal failure, where he popped up again and again after dissolving in a caustic sea again and again. We don't know if there's just one or even if it's normal behaviour. It probably is, but we have little data. Though I agree with your analysis, we have very little to substantiate it
Smashing the whole crystal to bits is only marginally better than not going at all. We'll get a moderately small and finite amount of crystal, which will diminish rapidly as we do even the most basic research into the discipline.
As per chapter 542, there's a lot of it. Not unimaginable amounts, but enough to get better and perhaps even enough to get a feel for types of materials that can work. At any rate, if we come back, we may see if the crystal is different, or if the piece that Hazō cut has regrown, but if it hasn't there's no reason not to take everything, prevent chakra golems from arising in the chakra-rich environment, end one of the sources of danger-to-humanity's-survival, etc.
I mention sentience because I have a strong preference against destroying a sentient life without good reason, and it's just plausible enough that the cave crystal might qualify in its own alien way that I would prefer we study it and make sure about that before we do anything that could be considered immoral.
That's good but there is no way that Hazō will be able to deduce that sentience unless it overtly communicates - and then there's the issue that it generates murderstatues, which, well, if it could communicate I would have assumed it do that first.
I don't think it's the cause of much death nowadays, since it doesn't extend its reach beyond the cave and the villagers nearby know how to stay safe around it.
They know how to stay relatively safe but they do seem to keep losing people to the "very hungry Lady Below." And anyone who doesn't do the necessary preparations apparently dies regardless.
But of course, the point is moot if there's no meaningful value in going there again in the first place.
I would argue "massive crystal that is our sole source of 3D sealing substrate" is good. Worst case scenario, if it's not enough for our purposes, as least Orochimaru can't have it.
The cave was remarkably docile at first, not even complaining when we chipped away some of the crystal. It only became aggressive when we attempted to Earthshape it, which we can avoid trying again
That's a fair point, my assumption was that it reacted to a whole, the same way a venus flytrap will snap only after several stimuli.
Shadow Clone makes this a lot safer
Iff they're in range. I mean it costs not a lot to try, but ultimately I'd want to argue for a "at the very least if the crystal is hostile again, blow it up for good with extreme prejudice" strategy.
And certainly, we can try out renewable crystal generation here at home.
Sounds to me like chasing after dreams tbh, we have nothing that points to "generation" but it certainly can be worth it if anything happens at all
I'd really rather not give Orochimaru 3D sealing hints, for the same reason we're not giving him FOOM.
(Joke)
Hivemind: "This poor being... if only we had some way of communicating with it."
Also the Hivemind: "Its bones can be used for 3D Sealing. Get 'em."
Technically, everyone's bones can be used for sealing.
[Jk] Shake Shika Down for Lore
[JK] Shake Shika from Side to Side
