Hm... if we were to use the Mangekyo Iron Nerve as the single parsimonious change, I can see that working fairly well, though it's not quite as suited to Hazou's present circumstances. The Jashin option provides a canon-supported power that would justify both Hazou's survival and in-person combat participation down the line, while directly enabling a viable Afterlife escape if we want to go that route. I'm not certain we could elegantly do all that with the Mangekyo Iron Nerve.
The issues any change should ideally address are:
*Hazou must be able to reliably participate in peer-level combats without the risk of death or being crippled for IRL months by a Severe. He should fairly quickly approach jounin level; there are simply way more interesting adventures possible as a jounin, and it's been nine freaking years. He shouldn't become an S-rank combatant because that would elide too much interesting content, but I feel like he's had plenty of chunin-tier adventures, having been chunin-level for like 500 chapters. Yuno-level combat power with great defenses would strike a good balance of risk-reward.
*Simulation burden on the QMs must be greatly simplified
*Incentives should be structured to actively go out and explore / adventure in the world rather than lighthousing. To a large degree this has already been addressed by the FP tax on prep days, but Runes are so powerful it bears keeping in mind.
I agree with
@Inferno Vulpix that, just as the Iron Nerve is a mutated, limited and inwards-turned Sharingan, so should its Mangekyo evolution be an imperfect mirror of its Uchiha brother's. There are several paradigms to interpret the powers of the Mangekyo Sharingan:
*Ultimate Three Ninja Arts - Tsukiyomi, the ultimate genjutsu; Amaterasu, the ultimate ninjutsu; Susano'o, the ultimate taijutsu
*Ultimate Offense, Defense, Utility - Amaterasu / Kakashi's Kamui, the ultimate offense; Susano'o / Obito's Kamui, the ultimate defense, Tsukiyomi / Combined Kamui, the ultimate utility
*Ultimate Self-Expression - Uchiha of the power-seeking Madara's line received the ultimate three ninja arts; Shisui the peacemaker received the ultimate 'diplomatic' tool; Obito the failure received the ultimate form of isolation
The Iron Nerve reflects only the "Copy" component of the Copy-Wheel Eye, with its domain of acquisition limited to the user's own movements (though if connected to another nervous system, would probably be able to access their entire history of movements - Oro would likely have wanted to investigate this). In terms of rough power level, it makes intuitive sense for me that the full powers of the Mangekyo Iron Nerve would be slightly weaker than the powers of a single Mangekyo eye - but, with the stress being distributed across the entire body, the physical cost is attenuated as well.
With that in mind, here's a proposal for Hazou's Mangekyo Iron Nerve. All numbers are preliminary and should be adjusted up/down for balance:
Mangekyo Iron Nerve
Pre-requisites: Kurosawa bloodline, Resolve 60, TYS 10+, suffer otherwise-fatal physical damage from a betrayal
Replaces the Iron Nerve
*The Iron Nerve user's natural talent in movement, hand-eye coordination, and kinesthetic arts of all kinds is augmented to a profound degree, comparable to the gulf between three-tomoe and Mangekyo Sharingan. Any Skill that benefitted from the Iron Nerve's +3 inherent bonus now benefits from a [+big number] inherent bonus instead.
*The user gains one power reflective of the Mangekyo paradigms and suited to their personality. Examples:
*
True Iron (Ultimate Defense, Ultimate Taijutsu): The user's entire nervous system becomes self-reliant and incredibly resilient, no longer dependent on surrounding biological processes. It produces its own chakra, being in all ways independent from the outside corpus. The user ignores physical Consequences that do not directly inflict damage upon this augmented nervous system, which has durability greatly scaling with the user's Resolve (Armor = Resolve AB, Stress Track = substitute Resolve for Physique; enemies unaware of the character's nature may inflict no damage if they attack nonvital organs). The intention is that the user is incredibly hard to put down for peer-level combatants, and well capable of surviving a defensive battle against superior opposition - though it does not suffice against truly devastating attacks like Amaterasu. With such resilience as this, one might even survive one's entire chakra system exploding!
-Like a zombie, damage to non-critical processes can be horrific yet remain almost-purely cosmetic. The user can develop techniques related to the growth, manipulation and alteration of their nervous system - think of Kimimaro Kaguya, but with chakra-metal nerves instead of bone. Examples include: rapidly regrowing damaged nerve segments, swords and nets made of nervous mesh, firing nerve tendrils into an opponent's body in order to hijack their physical movements, nerve tripwires that can be used to conduct Lightning jutsu, and (at the apex of development) straight-up downloading themselves into the CNS of their foe. This is represented by the Nerve Control skill, which is half-cost under Resolve. Breaking a combat stagnancy barrier grants the character 100 XP that may only be invested in the Nerve Control skill.
-Perhaps this was the true origin of Kagome's conception of the lupchanz...
-As a three-dimensional chakra-conductive structure, Hazou might be able to eventually form Runes out of his own nervous system, though this would require levels of Nerve Control commensurate to the complexity of the Rune in question. Now that's metal - a true S-Rank trick born of the natural synergy between one's inborn gifts and hard-won skills.
-This power offers a justification for Hazou's survival (for Human Path quest), or a source of shielded chakra regeneration and eventual runic substrate (for Afterlife quest)
*
Sheer Nerve (Ultimate Utility, Ultimate Genjutsu): The user enters a state of massively accelerated cognition within which they have perfect control of themselves and their chakra. This defeats any hostile genjutsu placed upon the user, as well as any hostile effect that could be resisted by Resolve; jutsu on the level of Tsukiyomi may contest this with an opposed check, though breaking through would require deific levels of power (Resolve x2 vs Genjutsu).
-While in this state the user is capable of flawlessly performing any movement or chakra manipulation that their body is theoretically capable of and which their mind can conceptualize. This grants [+big number] to all actions which could see their results improved by mental acceleration, perfect coordination and perfect chakra control, stacking where relevant with the inherent bonus of the Mangekyo Iron Nerve. This state is temporary and remaining in it for longer than a few objective minutes will inflict Mild physical and mental consequences; each time ladder up will increase the severity of the consequences by one tier.
-Alert, Ath, and Tai are all affected by the [+big number] buff, so this makes Hazou jounin-tier in a pinch. It's also applicable to Medical Ninjutsu, Technique Hacking, (probably) Minatosealing, Calligraphy, Carving, Earthshaping, and any other skill that relies on fine control and precision over raw might.
-The Sheer Nerve state can be flicked on/off for very brief periods for only a marginal cost in chakra. Perhaps this was the seed of Hazou's improvisational genius, only now flowered into an ability under conscious control.
-Primarily mental skills can be trained under the intense time dilation, if one has access to a relevant corpus of knowledge or teacher with super-speed. The user can basically read and memorize texts as quickly as they can turn the page, as each objective second is subjective minutes in their experience.
-This power doesn't really offer any justification for Hazou's survival, though it would probably be really useful in Afterlife quest if the memory-trading concept gains traction, as Hazou would be able to process foreign memories at extremely accelerated rates.
to install and take stuff…
