Point A: Have you ever seen the rain?

This detail first came to my attention through this reddit post. It has only rained once since the series started (in Chapter 3), and every single thing we hear about the weather before and since is that it is unseasonably dry. What's up with that? Has someone sealed the rain? Is this a ploy to free Nishino village by drying up the reservoir it's under? Who has the power to do that? Is it Seal? Or something more weather-specific?

As an artist, you're leaving symbolic money on the table if you don't let yourself have the weather match the characters' moods. If there's no rain in this story, you bet it's for a good reason.

Point B: A Kiss from a rose on the grey

Break is not an unfamiliar character to this series. They've had a chat with Asa, and also are the one to deliver a little bit of the power of Seal to both Minase and Yamaha. This raises an obvious question: what's the deal with Seal?

We know that the Seal twin of the last pair of twins to be born, 400 years ago, did not revive. What we don't know is why. Asa was given a choice to live or die, so perhaps he just chose death. But honestly, I don't know a lot of 7-year-olds who would do that, especially those with siblings to protect. This is a fact in need of explanation, and I'm dead sure that it will be important and plot relevant later. One hypothesis is that a previous Seal user used Seal to Seal their lifespan, and thus Seal is Sealed in some guy until further notice. If that's true, then effects that look like Seal effects, like the aforementioned rain, could be caused by this unknown third person.

This point is almost too big for this conspiracy board, but I've included it because I think there's a lot to support this theory. And since it can possibly help us explain other stuff I'll get to later. Such as...

Point C: Everybody hurts sometimes

...except Akio Kuroya. Why not?

In a series with less consistent metaphysics I'd say this was just a random character trait. But here? No chance. That shit's been Sealed. Even Yamaha says that's probably true:

But by whom?

The most obvious suspect would be Minase. Assuming that she's not lying about being Akio's mother (and we don't really have any reason to think she is, other than that she's generally quite sketchy) she would have the opportunity. And it does seem like planting Akio to be picked up by the Kagemoris was her plan, so she has the motive. But a question remains about whether she has the capacity. She can Seal lifespans, sure. But it has yet to be established whether she can Seal anything else. She has certainly never claimed to be able to do so, and she doesn't seem to have done something similar to any of her buddies. Yamaha even implies that Minase only has the power to seal lifespans, and that sealing pain is something that requires the full power of Seal. She's still the prime suspect, but I don't think the case against her is quite solid yet.

And even if the 'who' is certain, the 'why' is not. It's a pretty specific thing to do! It certainly helped Akio become a fighter good enough to get in good with the Kagemoris, but it was by no means a foolproof strategy for doing that. Akio himself notes that he could easily have wound up dead by now becuase of his lack of pain. It seems like there has to be more to this.

Point D: Hana's Mom has Something Going On

Some characters wear their tragic backstories on their sleeve. Some keep them a little more concealed. And some wear their tragic backstories under their sleeve, but the sleeve is a stretchy tracksuit and you can clearly see the outline of the tragic backstory through it. And some people mix their metaphors.

Hana's mother is for sure dead. Her pets are proof enough of that, as is her inhabiting of the Gravedigger role. But there's clearly more to the story than that.

We don't actually know that much about what makes Hana tick. We know what she likes (working out, sports, Jason Statham) and we know a little of what her life was like before all this (she's the only character in this whole series besides presumably the doctor who has definitely been to a university. Though I guess we don't know if she graduated). We know she's very protective of children, despite her repeated insistence that she doesn't like them. And we know that she's quite protective of elements of her predecessor's legacy, despite not conveying a lot of affection for that predecessor. She's kept that car in perfect condition for years.

This all points to a really complicated and difficult situation, in which Hana and her mom had a very troubled relationship and Hana does not know how to feel about her now that she's gone. I think the chances of us finishing this series without learning more about what happened here are slim to nil. (if you want to know my crack theory, it's that Hana's mom ditched her to marry Gonzo Kagemori, then died giving birth to Hikaru. This is not a good theory, I don't think the timeline works, I just like the thought of condensing two unknown dead mom characters into one).

Point E: Was Hydrogen Peroxide on sale or something? (Alternate joke: Bleach: Thousand Year Blood War)

This might just be a question with no further answer than 'it looks cool' but we have several characters with unusual hair colour patterns, and they all seem to be connected.

Dera, Ken, Roei, and Hana all have a white patch in otherwise black hair on their forehead. Hana has presumably dyed hers pink. Given that all three of these characters are from the Higashi Retainer Families, presumably that comes with the territory.

Oh, and also this random-ass ferry captain, who was specifically drawn taking his hat off to show us this fact. Wonder what that's about.

Notably, Mine also has some of the skunk-hair thing going on, just on a larger scale:

Then there are the red-and-whites, of which there are three:

As far as we know, there's no relationship between Left & Right and Misasagi. But the hair thing is suggestive. Of what, I have no idea.

Now, this could all just be for the sake of making the character designs pop on the black-and-white page. And indeed, Arakawa has said in interview that Left and Right were the first character designs she had for this series, because they were random designs she made while writing Fullmetal Alchemist. But I suspect there's more to it. As I suspect there is more to Misasagi's sick face tattoo.

Point F: What big teeth you have

Credit to @blorbologist for pointing this one out.

Gabriel has 30 teeth. That is, all the adult teeth except the third molars, or wisdom teeth. Again, this could just be an aesthetic choice, but given the detail and precision with which the teeth are rendered, I'm guessing it isn't.

Also, Gabby is the only person in the series besides the twins and their dad who has an unnatural eye colour (amongst colour page recipients thusfar. Though Granny Yamaha, and presumably Minase, have unusual light grey eyes). And unlike her red coat and blonde hair, which can be blamed on the Squenix PR department, her eye colour is clearly not an Elric hangover. That probably has something to do with something.

Point G: Big in Japan?

Perhaps the biggest unanswered question in my mind is 'what the heck is going on in this setting outside of Japan?' Are there daemons elsewhere? How are they involved in the rest of the world's conflicts? And if Break and Seal can only be born into these two specific villages in Japan, why is that? And for that, we have a little bit of insinuation to work with, but not a lot. I'll break this one down into subcategories.

Humans

The only character in this series who is confirmed to be from a place that isn't Japan is Ken's mom, who was Ethiopian. It's implied that she wasn't really involved in any tsugai stuff, though, so that doesn't tell us much.

However, there are two characters with names that might imply at least an overseas connection, and those are Ivan Yosano and Anna Mineyama. 'Ivan' is distinctly Slavic, and 'Anna' could be from almost anywhere.

(nb. All given names in this series are spelled out in katakana. Initially, I thought that the choice to spell 'Anna' phonetically, instead of using the kanji spelling that the Japanese name Ana typically uses was significant, but it doesn't appear to be so. Everyone's katakana only for given names)

Now, clearly both of these characters have Japanese family names. Mineyama's, in particular, uses the characters for 'mountain' and 'peak', which seems relevant to something or other. 'Yosano' has no obvious significance, other than that it's the name of a place and at least one interesting historical figure. But 'Ivan' is a conspicuously foreign given name, and Ivan's whole deal is at this point very mysterious.

Daemons

Most of the daemons we see in this story are based in Japanese mythology or folk tradition in one way or another, or have no precise origin. There are a few exceptions, though. Haruo's Tortise and Hare pair are, of course, from the Aesop fable. Sado-Masochist takes at least its name from the Freudian concept, and Judgement Day from the biblical one. Both of those ones are newly-made daemons, though, so that's less significant. The significant one is Mineyama's Soul Roller, the beetles. Because that is a mythological thing, and specifically an Ancient Egyptian one. So, there's some evidence that other mythology can give rise to tsugai. Those beetles are also basically the most consequential daemons in the whole series, so I'll come back to them later.

It's also worth noting that, on the (admittedly tenuous) assumption that Dera isn't lying, his daemons fought and died in a foreign war with him. Which does imply that at least some daemons are used in some combat outside Japan.

This may seem like a bit of an idle bit of worldbuilding speculation - after all, every story needs a setting, and at some point questions about what's going on outside that setting become uninteresting. When I was reading FMA, say, I didn't think that any major story point rested on the question of what was going on in the setting's equivalent of Australia. But here, it's different. Higashi village's stated goal is taking over the world. They might not know a lot about the world, but they sure do want all of it. And there's already been some explicit invocation of the rising sun imagery in the context of Higashi village, so I think it's pretty likely that Arakawa is including 'imperial ambition' in her list of critiques of their Medieval Times Death Cult LARP culture.

Also, when Asa meets Break, Break has to consult their library to get the name of the place Asa is in Asa's language. Which does rather imply that people can come there from places that speak a different language, doesn't it?

Point H: Why don't we know this bandit's name

Comiserations to the poor unfortunate wiki editors.

Point I: The Deep State

This one, admittedly, is more of a full theory than a loose end.

Did anyone notice how the MiB/Aliens just... invited themselves on Asa and Yuru's Okinawa vacation?

First they overhear Asa suggesting it. Because they were listening in on Yuru's previous conversation from the bushes.

And then the next we see is...

One of them surprises Asa when she's leaving. As if she didn't really expect them to be there. Asa does go along with it, though.

Yuru later confirms that he also did not invite them. So what are they doing there? They claim they're 'guides', but in the same breath they claim that they've never been on a boat before, so they can't be very good guides.

They're kind of a strange presence in the story overall, right? So far their main narrative function has been to serve as comic relief and occasional exposition, but from a Doylist perspective, that's a bit of a weak justification for two-and-a-half extra characters in a whole bunch of important scenes. And their Watsonian justifications for their actions are also always a bit flimsy - just fangirling over L+R or the Zashiki-Warashi or Oshira-sama. It always puts them right in the center of whatever's going on, though, especially where Yuru is. They even gain entrance to the famously untrusting Dera's place just by hanging out with Danji for a bit. They're suspiciously good at not being suspicious. They also oscillate frequently between 'knowing things about the modern world' and 'not knowing anything about the modern world'. They don't seem to have any contacts besides our main characters, despite being very friendly, and they don't have any obvious way to get money, despite frequently noting that they need to buy dog food.

And hey, the pirate guy did say that Asa had been tailed by a public safety commission member from the moment she left the Kagemori manor...

Listen, I'm not saying that the Aliens disguising themselves as Government Men-in-Black are actually Government Men-in-Black disguising themselves as Aliens disguising themselves as Goverment Men-in-Black, but I do think it would be a hell of a twist. And these are all loose ends that need tying up. Perhaps this particular theory is wrong, but I do think that there's something up with these guys.

Point J: Granny Yamaha is Bad At Her Job

Granny Yamaha is an interesting paradox of a character, right? She's sort of a villain but not quite, and a lot of the bad stuff that happens here is directly her fault. And yet, she doesn't really seem to want to take over the world, as is the supposed mission of Higashi Village. Or if she does, she's really bad at it.

Yamaha's stated motivation is this:

She wants to protect the village from external threats. Fair enough. But if that is her goal, three things remain unexplained. First, why has she not contracted any daemons of her own, and instead leaves her own protection to the daemons of her lackey; second, why do none of the other villagers have daemons or even the ability to see them; and third, why is the amulet necessary to contract with Right and Left, the village's guardian deities, in the hands of Dera, a guy who is there roughly every two weeks? For someone who has had a lot of time to set up defenses for the village she claims to want to defend, she sure is bad at it. It's been the site of two massacres in as many in-world weeks, and there doesn't seem to be a damn thing she can do about that.

There are a couple of ways to explain this away. She could just be suffering from a terminal case of hubris, as most people would after 400 years. I say she's bad at her job, but her strategy did work for the entirety of that time, and only stopped working because Asa came back with Break. It could be paranoia, too - she saw the village almost get wrecked by bad governance, caused by one guy with too much power via his daemons. If the villagers don't know about daemons, they can't challenge her power.

Or, of course, there's the other possible inference - that what she claims are her goals are not actually her goals anymore. Perhaps she's trying to bring down the village herself, slowly, from the inside. Perhaps she's even aiding and abetting Minase's grand scheme to resurrect Nishino Village. She was certainly very happy to see the twins, after all, and very protective of them...

Point K: Coming Out of my Cage, And I've Been Doing Not Great

...speaking of which, why was Asa in that cage in the first place?

This is Fake Asa, of course, but Real Asa was also stuck in there the whole time, for reasons that have never been adequately explained. The story that Yuru was given was that it was her 'duty', but no such duty has ever been presented to us.

What's with the cage? Seems a little extreme if the point is just to protect her. Does it have something to do with Asa being the Day Twin and Yuru (who goes outside in the day all the time) being the Night Twin? If so, what's the rationale? Trying to manipulate Asa into wanting to Break out of there?