Very fun update,
@eaglejarl @Velorien @Paperclipped ! I personally would like a continuation with the following traits:
*Preserves simulationism: The solution minimizes retcons; story continues onward with as much of this update canonized as possible.
*Preserves PoV: Hazou's perspective and role as mc continue.
*Feels Earned: The solution is both adequately foreshadowed by prior worldbuilding AND is a result of player action within the rules of that worldbuilding
Fortunately, there are at least two solutions that possess all these traits!
I. The Jashin Option
Plausibility: High, if Jashin is the 'washer' entity in Kamehameha's speech
As others have mentioned upthread: if the washerman is invested in the flow of souls between paths, and Hazou's EM proliferation switch goes off, the flow of souls will be permanently interrupted by the cessation of life on the Human Path. Luckily there is a very convenient solution to this which is both timely and, of all things, supported by Naruto canon!
If Hidan is in the Pure Lands, then Hazou may be the most powerful Jashinist on the Human Path. Moreover, he has just - at direct player behest - successfully sacrificed many lives to Jashin in a single cataclysmic burst, with his prayer and dedication prior to firing the RER barrage. Furthermore, Jashin has a strong vested interest in Hazou's death not coming to pass.
One could argue, therefore, that Hazou has just fulfilled the requirements to attain Hidan-style immortality, becoming Jashin's prophet on the Human Path.
And the prophet of Jashin cannot be slain by mortal hands.
Pros:
*Adequately foreshadowed by prior worldbuilding and existing Naruto canon
*Earned by direct player action
*Congruent with Hazou's immense achievements and longstanding relationship with Jashin
*Ironic yet appropriate timing
*Elegant - no retcons necessary as long as King Kamehameha was right about the 'washer' entity and the washer entity is Jashin
*Bonus - Hidan-style regeneration lowers the stakes of in-person combat and makes Hazou a virtually priceless combat asset, creating strong incentives for Hazou to participate directly in combat scenes
*If Hazou has Hidan-style regeneration, many portions of the setting do not have to be modeled as closely / with as much care, because they become less relevant on the margin
Hazou's remains begin to stitch themselves together - slowly, imperceptibly, then all at once. Hazou must navigate this post-betrayal world, avoid capture by Orochimaru (regeneration is no guarantee of relevance), contend with Akatsuki and organize matters in Konoha and beyond.
II. Mangekyo Iron Nerve
Plausibility: Pretty High
This scenario was a genjutsu / psyop by Orochimaru intended to spark the Mangekyo Iron Nerve in Hazou. Orochimaru knows how to do this from his experimentation on Ren. Why does Orochimaru want to spark a free powerup for Hazou?
Because immediately killing Hazou at this juncture isn't actually in his best interests. The ideal world for Orochimaru is one where all world-ending threats are contained or neutralized and all major powers are eliminated or subservient to him. Were he to slay Hazou now and depart with the rift, he would be hunted by the full force of Leaf and Akatsuki without the distraction of the Goketsu splitting their forces and attention. That is a level of heat he's survived before, but not while also perpetually guarding a mostly-static interdimensional rift. There is even the (small but nontrivial) risk that Akatsuki somehow believe Leaf and the two adversaries combine forces to hunt him.
If Oro simply buries the rift in a volcano or something, there's the risk that Itachi detects it with his cheating eyeballs or an exotic Crow technique, or that a Hyuuga THer finds it, or that Leaf's sealmaster corps (or Sasori) produce seals capable of locating it. As time goes on, the chance of Nagato being on the other side of that closed rift increases, so he suffers mounting existential risks each day the rift stays unguarded. Any guard less than himself would barely deter Akatsuki.
If he has to stay moving with the rift while also on the run, he can't build a comprehensive lab or power base and has to continually invest nontrivial amounts of chakra in rift-kicking and moving runes. If he holes up in one place, he leaves himself vulnerable to being Zoo Rushed or Amaterasu'd from range.
Therefore, it is in Orochimaru's best interests for Leaf and Akatsuki to exhaust each other - ideally, destroy each other - and have no energy to spend chasing him. As he currently believes Akatsuki to have the edge in that contest, powering up their chief antagonist while maintaining an effortless killswitch is the optimal move.
Oro's ideal timeline is this:
Week 1: Oro is 'moving the rift to Leaf.' Hazou, now trusting uncle Oro even more than before, returns to Leaf to fortify it against aggressino
Week 2: Akatsuki forces assault Leaf, Hazou's Runes allow Leaf to bleed Akatsuki and ideally kill several members. Oro makes plausible excuses for why the Rift hasn't arrived yet.
Week 3+: Oro's treachery becomes apparent, but Leaf and Akatsuki have expended all their dry powder against each other in Week 2. Only after confirmation of events in Leaf vs Akatsuki does Oro trigger the bioseal in Hazou, killing him.
I would therefore argue it is more plausible for Oro to wait until Week 3+ before triggering the bioseal. Akatsuki already knows Runes exist (they participated in the Dragonwar) and won't be able to reverse engineer anything from Hazou's rune blanks just as they weren't able to reverse engineering anything from the Great Seal, which was a much more comprehensive 'primer' on the subject. Leaking the specific datum "the now-dead Hazou was capable of creating Runes" to the surviving Akatsuki is more than worth the average cost in Akatsuki lives Hazou's offensive Runes would reap - and more importantly, maintaining the status quo for a few weeks more ensures that Leaf and Akatsuki remain at each other's throats while he gets away, while creating the explosive new variable of Hazou's death generates far less predictable outcomes.
It is consistent with Hazou's characterization in previous plans that he would seek to have the bioseal removed ASAP, and this would give the players a bit of time to invent a solution (more time than Oro anticipates, given the existence of TR).
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My preferred solution? A combination of both! After Jashin regenerates Hazou, the massive emotional trauma of Orochimaru's betrayal would naturally have awoken his Mangekyo Iron Nerve! It is somewhat overdramatic for Hazou to get two huge buffs out of this but that's just how the simulationist dice roll sometimes - it was already well-established that Mangekyo requries massive emotional trauma, and Hazou hadn't sacrificed an immense number of lives to Jashin (while Hidan was absent from the Human Path) until just recently.
Even better if the Mangekyo Iron Nerve grants large, immediate combat-relevant buffs that would further justify Hazou's presence on kinetic missions.
The afterlife continuation sounds cool but would require more nudging - either a chakra oasis or some kind of workaround for Hazou's powers to stay relevant in the Pure Lands, lest he be consigned to merely Hidan's sidekick with mostly-useless theoretical knowledge.
The Jashin Option, on the other hand, works completely within the textual evidence as presented by previous updates, and would easily allow for future combats with less terminal stakes! Stakes wouldn't be eliminated since Hazou could still be captured, but 'being captured' is not a quest-end scenario so the players will be more likely to vote for lines of action that involve combat.
