"Also for 'kids are dumb' reasons. You basically need to be constantly supervising very small kids to make sure they aren't getting overexcited about magic, and not every family can do that - or recognize if a kid is even using magic."

"The norm in my state, Konoha, was that children could test into the Academy, from any family - the kids were told the entrance exams were about things like reading and math and physical ability, but those were more placement tests with some medical evaluation mixed in, and instead we'd be put into situations that let the teachers evaluate things like our impulse control, caution, self awareness, and ability to follow directions while we didn't know we were being watched. That system isn't perfect - subjective judgement introduces chances for bias, if nothing else - but it mostly works, and then you also educate the parents about chakra exhaustion. We did also though require all families with students in the Academy to live within the village walls, where most shinobi lived, which patches some stuff too - Konoha has a really pro-family culture, and shinobi especially tend to not mind parenting random kids."

"It doesn't scale perfectly, though, especially the parts leaning on just having ambient adult shinobi around. Still, most Academy kids hit the cut offs between six and nine - but we're finding now that kids who aren't raised around shinobi can hit those milestones later than we'd like, and tend to be a lot more likely to experiment on their own, and the drop off in potential gets pretty bad from six to about fourteen."

"Also Konoha shinobi are apparently really, really unusually inclined to parent random children, we're having - culture issues, with everyone else, and there's a wider gap between civilian and shinobi cultures in most nations than there is in ours, which adds to parents being reluctant to have their kids trained."

"That sounds rough and not the sort of thing you can import along with a combine harvester, alas."

"Yeah."

"Some of the other nations think we should be starting residential schools, but unfortunately for them Konoha is the most populous shinobi nation and we are not child thieves and we're also the only ones who already had programs for civilian-born shinobi, so they can - "

She pauses and collects herself. "...Thing that is improper and undiplomatic to say, especially when I don't know your culture's opinion on vulgarity."

Not really pausing for comment: "But we can get decent effects teaching ten through fourteen year olds, and female civilian kids do better earlier on self control metrics and that's the only major point where you get long-term societal impacts from which age education started at. And we don't need everyone up to traditional standards, anyways, and then the next generation will have more shinobi parents."

"Right. Do you suppose people from here can learn?"

"No idea! You don't feel like you have chakra, but - that's not always conclusive..."

"Me in particular or anybody?"

"The other humans I've passed here haven't, either."

"And you won't have seen a wildly unrepresentative sample. That's not a guarantee though? What else would be going on?"

"Your world doesn't have chakra in general, as far as I can tell. I still do, and my chakra feels like it's replenishing, but that might be a world origin thing. Maybe anyone who visits my world will get the ability to use chakra if they try hard enough. Maybe you have to be born there."

"Something supporting that at least a little is that the kids of an active shinobi woman tend to have a much easier time reaching for and using chakra, as well as developing larger chakra reserves and the like, than the kids of civilian women. Which suggests that being around or interacting with chakra at critical development points can be in general fairly important... But early chakra exposure could just end up making the difference between 'can learn easily' and 'has to work hard,' rather than determining if you can learn at all."

"Maybe in addition to selling us magic items you'll have a... gestation tourism industry, too."

"Kids would have to stick around to get training; you really don't want to experiment with it on your own. But most places will probably be willing to set up at least some immigration... But at first probably not a lot, and probably favoring people who would be cultural fits. Especially not until we get our own population caught up."

"Would they actually have to stick around, or could some training move here?"

"Maybe in a few generations, but we don't have the spare people, and - "

"Chakra use is... Not exactly sacred but it's really hard to convince people to teach others from their own nation. And a lot of the older traditions were actually explicitly religious, and - you don't teach outsiders."

"Both as a cultural thing and as a security concern. Magic's a weapon; you can't have a trained chakra user who shouldn't be treated as constantly armed with high explosives, and people with high explosives are actually a lot easier to contain and can ever be meaningfully disarmed."

"This isn't a problem in a shinobi village - shinobi can defend against each other - but. Civilians can't really defend against us."

"Hrm. Well, here we have eclipsed, but I can see where a certain insularity would have come from."

"It might change with time, but I'd expect immigration to be allowed way, way sooner."

"Probably there will be some of that too. Uh, how would your world be at tolerating a refugee influx, there's occasionally issues where there's a hurricane or a civil war or whatever and people don't have any place that wants to take them?"

"Depends on what they need, but our entire population is currently basically refugees - we don't tend to have cultural issues about excess population or more people to trade with, though we might have logistics issues if people need more support than 'over there's some land no one's using, have at it'... But if we can get our land fertile again, we'll very suddenly have way more land and food than we have population or ability to fill it."

" - Oh, and, another thing that'll encourage leaders to support less restrictive immigration - chakra-use training reduces fertility kind of a lot, and shinobi women miscarry more than civilian women reproducing with civilian men - but less than civilian women with shinobi men. It's not a problem for population stability when you get infant and maternal mortality low and have good prenatal care, but without aggressive pro-natalist policies plus folding in civilians, shinobi populations don't really grow on their own. A flow of immigrants will allow us to get a lot more of the overall population trained without risking demographic collapse than we could otherwise."

"My - somewhat hopeful, mostly objective, projection is that there'll be some pilot immigration programs with people who are very good cultural fits and want to assimilate, which'll also serve as a 'does anything go horrifically wrong if aliens try to live on our planet' experiment, and by the time the first wave's kids have been getting training for a year or two, the younger leaders will be pushing to open borders more, making a counter-force politically against people who'd prefer cultural stability."

"Just... For all we know, moving to our planet if you were born elsewhere gives you cancer, or pregnancy on our planet if you were born elsewhere has an even higher maternal and fetal mortality rate than couples with a civilian mother and a shinobi father, and we'd rather find that out before importing massive numbers of people. And we'd rather import people who won't object to our entire way of life, or who won't decide we need to be changed and do what they do instead."

"That going well will also depend on diplomatic relations remaining stable, but - people on our side will be pretty motivated."

"It would be pretty weird if you looked exactly like the same species as us but also didn't get cancer from something that gave us cancer, but I suppose we could be looking at something like an infectious disease issue, that's a fair reason not to go full bore right away."

"...Oh, yeah. Diseases might be weird. Shinobi don't get sick unless we're constantly running on low chakra, but there's stuff that sometimes flares up in the civilian population. Mostly just things that're fixed by improved infrastructure for clean water, but it's not nothing."

"It could also be that all our subpopulations who respond to 'sudden chakra influx' with autoimmune issues or whatever died out before recorded history, though. You can get major differences in susceptibility to disease without full species divergence."

"Yeah, that's true, maybe we are all the celiacs of chakra."

"Especially since foreign chakra can cause autoimmune or related issues - that's why the issues with pregnancy. Developing fetal chakra can interact violently with maternal chakra, especially since fetal chakra is inherently unbalanced. Women with very good chakra control can manage this, but not untrained women, though purely civilian-born kids don't develop a detectable chakra capacity until after birth and so civilian-civilian pregnancies don't trigger the same problems."

"...Probably. It just occurred to me we might have significantly different miscarriage and maternal mortality rates from your world."

"Fifteen to twenty percent miscarriages, defined as any loss in the first twenty weeks, and very rare death in childbirth, less than twenty per ten thousand."

"Shinobi women in Konoha medical systems tend to miscarry around thirty percent in the first trimester, thirty to fifty percent in most other shinobi medical systems, forty to sixty percent in non-shinobi systems or without medical care. Chakra incompatibility issues don't hit until the second trimester usually, and very rarely hit shinobi women - they actually hit shinobi women in better medical systems more often, we think first trimester miscarriages might be mostly due to incompatibility. Shinobi women who make it to the second trimester with no medical care usually don't have a problem, and first trimester miscarriages don't tend to be associated with maternal death - a couple of patchier medical systems don't bother with prenatal care because of that. Generally you'll lose about another five to ten percent in the second trimester."

"Civilian women miscarry around twenty five to forty percent depending on medical care and nutrition - that might be complicated by our nutrition levels, though, the twenty five percent mark is for women in Konoha which can actually keep its population fed. Civilian women whose children had shinobi fathers miscarry at about the same rates until the second trimester - probably we could get 'ability to keep preterm infants alive' down to meet the usual onset of major problems. We're nearly at that in Konoha - we're down to twenty one weeks as usual cutoff for viability, problems usually start hitting from sixteen to twenty three weeks - but everywhere else struggles significantly with preemies before twenty five to twenty seven weeks."

"Problems usually worsen over the second trimester - overall about a fourth of pregnancies between civilian women and shinobi men that weren't intentionally terminated make it close enough to term for the infant to usually survive. That rises to half in Konoha, with we think lower abortion rates - though we don't have anyone else's concrete data on those."

"Maternal mortality with pure civilian couples is a bit under ten per one thousand live births in areas with worse medical care, something like a thousandth that in Konoha. Civilian women with shinobi men tends to increase maternal mortality by a factor of ten. So, we strongly discourage it but don't ban it in Konoha, since our usual rate is effectively a rounding error. Other places have different policies. For shinobi - I actually don't know of any shinobi who died in childbirth who didn't have seals collecting or storing dangerous foreign chakra in their bodies that ruptured due to the pregnancy. Sealing dangerous foreign chakra into your own body is dumb, by the way, don't ever do that. Rates for dying in childbirth due to making dumb decisions about seals are 'of the five people we know who tried this, three definitely died of this and one was severely ill but then was murdered before she could get medical care.' Last one we think would have been fine without the murder. Which is a reason to not do that, but otherwise not really conclusive."

"I'm impressed you have all that memorized."

"I'm a doctor. Not centrally trained as a gynecologist, but I testify before the council of nations a lot and advise the leader of Konoha, so I've been cross-specializing in - basically everything policy relevant, at least to the point where I can tell them which experts they need to bring in instead. And those experts then usually want me presenting alongside them or at least helping them with their arguments; there are very few medics fully comfortable with politics."