The Theory Thread

[Raikaria]

Just a thread where people can post and discuss theories about Touhou characters. After all, many characters have things left unexplored, questions unanswered, ect, ect.

Theories have to be reasoned. For example just saying 'Sakuya is a Lunarian' isn't cool. 'Sakuya is a Lunarian because of *Explained events in IN*' is cool.

Theories can be as off-the wall and extreme as you ish, as long as they can be backed up.

I have several theories about characters, but I'll share what I feel is my strongest one.

Elly's species was never revealed. She is just... a Youkai.

However, I think there is a lot of evidence pointing to her being a Shinigami, or, more specifically, an equivalent personification of death.

1: Her weapon is a scythe. This is akin to Komachi, and Scythes are the generic weapon of the Shinigami.
2: Her theme is called Perdition Crisis. Perdition's Definition:

Noun
(in Christian theology) A state of eternal punishment and damnation into which a sinful and unpenitent person passes after death.

So her theme is hinting at Death, Purgatory, and Christian believes.

3: Elly's appearance is somewhat similar to that of the Ankou. The Ankou is a Breton personification of Death. The Bretons were Catholic, forming a tie with Perdition as a Cristian theological term.

'who appears as a man or skeleton wearing a cloak and wielding a scythe and in some stories he is described as a shadow that looks like a man with an old hat and a scythe, often atop a cart for collecting the dead. He is said to wear a black robe with a large hat which conceals his face.'

While Elly is not a skeleton, has no carriage, and is female, and wears red and white, she fits the description somewhat.

Piecing all three together, it seems reasonable to assume Elly is a 'Shinigami' or some equivalent [Since Eiki is the Yama of Gensokyo, maybe the Yama of Brittany would have different henchmen?]. Which in itself raises questions. Why is she working for Yuuka? Why isn't she under the service of the Yama? Does Yuuka have a connection with the Yama?

Ironic that like Meiling, a fellow Stage 3 boss who is a gatekeeper, Elly can be theorized to be something more powerful than she is shown. Except the reasoning for Shinigami Elly is stronger IMO than 'Actually a Dragon' Meiling.

[ShiroiMahotsukai]

I like to think that Elly is a scythe. She's a Tsukumogami. That's why her scythe functions as a boomerang, because it's her real body. In a sense I think of her as being the same as Kogasa.

[ToyoRai]

Oh, this is gonna be fun.

So ihave a theory that the reason why Yukari is so lazy is because her boundary manipulation takes a lot of strenght to do, and she usually doesn't have that much energy in her, meaning hse has to sleep alot to have any inch of energy. I mean, think how much energy it would take to screw with the laws of nature, time and space and all the other stuff. Heck, if we would believe the reason why Yukari is so old is because she is messing with the Borders of Age, it would mean she is constanly using her pwoers to do at least one thing.

[hind]

Sounds stupid, but I think Remilia manipulated Meiling's and Sakuya's temperaments via fate. This explains why Meiling is so human-like in nature and why Sakuya...isn't? It still needs some fleshing out but I think I have the main idea down.

[Darkness1]

Ironic that like Meiling, a fellow Stage 3 boss who is a gatekeeper, Elly can be theorized to be something more powerful than she is shown. Except the reasoning for Shinigami Elly is stronger IMO than 'Actually a Dragon' Meiling.

It is very possible that canon Elly is a shinigami, or as I would say, was and is now retired to work for Yuuka. Yes, this makes Elly very powerful, but if Meiling actually was a dragon, it is questionable if she really would be stronger since dragons are known to be insanely powerful in the touhou universe.

I like to think that Elly is a scythe. She's a Tsukumogami. That's why her scythe functions as a boomerang, because it's her real body. In a sense I think of her as being the same as Kogasa.

Is also possible, but I don't see it as plausible as the other theory myself. Wouldn't Elly take damage if her scythe blocks bullets in that case? Because I don't remember that happening in the game. I haven't really read most of the dialogues from the pc98 games so I may be wrong.

This also applies to other ancient youkai, like Akyu states in PMiSS: "As youkai live longer, they become less active." Other than that, interesting theory, I have no other argument against it.

[Tengukami]

I would be really, really surprised if anything about Elly turned out to be inspired by British culture, or Christianity in general.

[Clarste]

Theory: The tengu village used to be something like a ninja village until it was re-purposed into newspapering. I mean, a secret village in the mountains where residents are put into castes and trained from birth to do their one job? "Information Gathering Corps"? The whole thing just screams "ninja village". Not to mention the whole concept of ninjutsu is often attributed to people being taught by tengu, so it stands to reason that tengu are the original ninjas. Ergo, Aya (who is over 1000 years old) must be a retired ninja trying to put her old skills to work in a new form.

[commandercool]

Theory: The tengu village used to be something like a ninja village until it was re-purposed into newspapering. I mean, a secret village in the mountains where residents are put into castes and trained from birth to do their one job? "Information Gathering Corps"? The whole thing just screams "ninja village". Not to mention the whole concept of ninjutsu is often attributed to people being taught by tengu, so it stands to reason that tengu are the original ninjas. Ergo, Aya (who is over 1000 years old) must be a retired ninja trying to put her old skills to work in a new form.

Isn't that more a case of "ninjas are humans imitating Tengu" than "human ninjas are a thing and Tengu ninjas are a thing, and human ninjas are humans imitating tengu ninjas"?

[Darkness1]

Theory: Gengetsu and Mugetsus domain is the world of nightmares, kind of. Both their powers would act to this nature. The midboss is Nue?

Theory2: The satoris are the eyes, the bodies are just hosts used for travel, communication and such.

Theory3: Konngara is one of the four devas?

[CyberiAccela]

I don't think Konngara is one of the four devas.

I think it's kind of a "pillar men" sort of horn thing.

Yuugi has one, Suika has two, I'm willing to bet there's something about Kasen's arm that would count it as a third (aside from the two that are obviously under those things in her hair), which means there's a four-horned (or "horned", if Kasen's arm counts but isn't literally a horn) oni out there somewhere.

Maybe.

[draganuv15]

Yeah, pretty sure Konngara isn't even an oni. Isn't she a Yaksha?

[Darkness1]

Yeah, pretty sure Konngara isn't even an oni. Isn't she a Yaksha?

Actually, yeah. I was wrong there.

[ToyoRai]

Yeah, pretty sure Konngara isn't even an oni. Isn't she a Yaksha?

When the heck has that been stated?

@Kasen What? Why in Former Hell would you think she has a horn in her ARM?

@Mugetsu and Gengetsu I always think that Mugetsu is sort of ruler of dreams and Gengetsu is ruler of nightmares. Mugetsu is self claimed ruler of Dream World so that would make sense, and Gengetsu is a freaking devil with the appearance of an angel who becomes a nightmare to fight if you let her last long enough.

[draganuv15]

When the heck has that been stated?

Probably somewhere in HRtP's manual. I know it's been stated somewhere and that's what the wiki says -_('_')_-

[Tengukami]

I'm going to contribute on behalf of Tiamat now, posting my personal favorite fan theory of all (and one that I've posted many times before as an example of a well-constructed fan theory), a.k.a., Yukari Was Maribel.

[ToyoRai]

Probably somewhere in HRtP's manual. I know it's been stated somewhere and that's what the wiki says -_('_')_-

Yeah, believe something which even the wiki says it needs a reliable source. Note, I posted the comment udring a time which I couldn't get into wiki, so that's why I was questioning that on the way I did.

[Sagus]

Yeah, pretty sure Konngara isn't even an oni. Isn't she a Yaksha?

Yaksha is what Konngara Doji (as in, the attendant of Fudoo Myoo-oo) is said to be. There's no proof that touhou's Konngara is supposed to be him, so saying that she's a yaksha makes no more sense than saying that she's an oni.

HRtP doesn't have character profiles, by the way.

[CyberiAccela]

@Kasen What? Why in Former Hell would you think she has a horn in her ARM?

I don't think she has a horn in her arm, I just think it's supposed to represent a third distinguishing feature like a "horn" in some way.

It made more sense in my head.

I'm not giving up on this pillar man parallel til we see her horns!

[Sagus]

I'm going to contribute on behalf of Tiamat now, posting my personal favorite fan theory of all (and one that I've posted many times before as an example of a well-constructed fan theory), a.k.a., Yukari Was Maribel.

This theory needs a little modification near the end, since we know, with the new cds, that Maribel's powers are now strong enough to transport her and Renko to other worlds, so the trigger that turned her in to Yukari can't be that.

[ToyoRai]

Theory: Yoshika was buried in the area where Gensokyo was formed in.
Reasoning: In SoPM, Akyuu states that Yoshika isn't from this era, and no one knows her. However, if she was buried in Human World, I don't think she would have served that great of a memory to people to cause her corpse to be tranported into Gensokyo if she was forgotten like Miko. So unless Seika brought Yoshika with her once she entered Gensokyo, which I find unlikely, her grave would probably been in the general area where Gensokyo was formed in so that her copse would have been transported into it and to be discovered by Seiga later on. That, or Yoshika is one of the first humans to have lived in Gensokyo but was not remembered by the other people.

[Sagus]

Eh, I don't think it's that unlikely for Seiga to have brought Yoshika along with her; it's at least more likely than her having been buried there before Gensokyo's existence, since it takes little over a year for even a buried body to be nothing but teeth and bones. So unless her anti-rot charm can also reconstruct flesh, Yoshika would be a walking skeleton, not a jiang-shi.

My theory is that Yoshika is the 9th century poet Miyako no Yoshika (she has basically the same name, and is know to compose poems when she's without her ofuda), and Seiga (who, having at least 1400 years, would already be an hermit by then) liked her poems so much that she killed her by poisoning (suggested to be Yoshika's cause of death in SoPM), so as to not destroy her physical appearance, and kept her around as a pet ever since then.

Certainly not the worst thing the fetus lady did in her lifetime, I"m sure :V

[Clarste]

Eh, I don't think it's that unlikely for Seiga to have brought Yoshika along with her; it's at least more likely than her having been buried there before Gensokyo's existence, since it takes little over a year for even a buried body to be nothing but teeth and bones. So unless her anti-rot charm can also reconstruct flesh, Yoshika would be a walking skeleton, not a jiang-shi.

My theory is that Yoshika is the 9th century poet Miyako no Yoshika (she has basically the same name, and is know to compose poems when she's without her ofuda), and Seiga (who, having at least 1400 years, would already be an hermit by then) liked her poems so much that she killed her by poisoning (suggested to be Yoshika's cause of death in SoPM), so as to not destroy her physical appearance, and kept her around as a pet ever since then.

Certainly not the worst thing the fetus lady did in her lifetime, I"m sure :V

While I don't think Seiga is above poisoning someone, I also think she's smart enough to realize that there's not much point in keeping a poet around when her brain is rotted away and she doesn't do poetry while under Seiga's control. I like to think they were friends (insofar as close as Seiga can truly be friends with anyone) and after Yoshika's death from another person's poison she kept her around as a memento. A "person she found interesting".

[Prime32]

I theorise that Sanae is a Vocaloid fan, and that this influenced the design of her miko outfit. Reasoning: Sanae is a geek, and in a world without Touhou then Vocaloid would have the largest doujin output of any franchise. :V

Heck, if we would believe the reason why Yukari is so old is because she is messing with the Borders of Age, it would mean she is constanly using her pwoers to do at least one thing.

Yukari isn't really that old though, by youkai standards. As in, Eirin and Tewi are thousands of times her age. We know she was around before the Great Hakurei Barrier, but so were a ton of other characters.

[Sagus]

Eirin isn't a youkai, though, and Tewi's age is only vaguely implied to be really big.

But yeah, as far as we know, Yukari isn't particularly old among the "top tier" youkai in Gensokyo.

but who knows how far back in time Maribel ended up before turning into Yukari

maybe she even witnessed the birth of the oceans  :getdown:

[Raikaria]

I would be really, really surprised if anything about Elly turned out to be inspired by British culture, or Christianity in general.

Not out of possibility. We have Yumemi's Crosses in Touhou 3, Gengetsu and Mugetsu have cross imagery, and Gengetsu is like an angel. Shinki is basically satan. There's actually a fair amount of Christian symbolism in the PC-98 era.

Plus the meaning of Perdition is from Christian theology. There's a Christianity reference as her theme name. Also, Brittany isn't Britain. It was a Celtic nation, but it's actually part of France, but had heavy migration of British before.

Oh, this is gonna be fun.

So ihave a theory that the reason why Yukari is so lazy is because her boundary manipulation takes a lot of strenght to do, and she usually doesn't have that much energy in her, meaning hse has to sleep alot to have any inch of energy. I mean, think how much energy it would take to screw with the laws of nature, time and space and all the other stuff. Heck, if we would believe the reason why Yukari is so old is because she is messing with the Borders of Age, it would mean she is constanly using her pwoers to do at least one thing.

Could be plausible. However, she also seems to not be worn out after using border manipulation in most cases she's been shown using it. Might be a facade, of course.

It is very possible that canon Elly is a shinigami, or as I would say, was and is now retired to work for Yuuka. Yes, this makes Elly very powerful, but if Meiling actually was a dragon, it is questionable if she really would be stronger since dragons are known to be insanely powerful in the touhou universe.

Meiling, if she was actually a Dragon, would probobly be stronger than she lets on. Personally I don't like that wagon *too* much, other than 'Hong' being like 'Long', which is Chinese for 'Dragon'.

Theory: The tengu village used to be something like a ninja village until it was re-purposed into newspapering. I mean, a secret village in the mountains where residents are put into castes and trained from birth to do their one job? "Information Gathering Corps"? The whole thing just screams "ninja village". Not to mention the whole concept of ninjutsu is often attributed to people being taught by tengu, so it stands to reason that tengu are the original ninjas. Ergo, Aya (who is over 1000 years old) must be a retired ninja trying to put her old skills to work in a new form.

We only know of three Tengu, one is a Wolf, who is clearly a scout/warrior. The other two are reporters, and it seems Aya and Hatate don't have any other competition than each other, judging from their rivalry. Also, Tengu society seems very rigid. Also remember they used to be bossed around by the Oni, but somehow overcame it.

I'm going to contribute on behalf of Tiamat now, posting my personal favorite fan theory of all (and one that I've posted many times before as an example of a well-constructed fan theory), a.k.a., Yukari Was Maribel.

Yukari-Maribel is oozeing potential. I think it's unlikely Maribel IS Yukari, as they both exist at once, and at the very least, HM shows Yukari awake during the day, meaning Maribel would be asleep during the day. I think a relationship exists, but they are not one and the same.

Unless timey-wimey shenanigans. Always possible with Gaphax I guess. However, we also know Yukari's been alive for quite a while. My personal guess is Maribel is related to Yukari, but is not Yukari herself. We know Human-Youkai hybrids can exist, look at Rinnosuke.

Yukari isn't really that old though, by youkai standards. As in, Eirin and Tewi are thousands of times her age. We know she was around before the Great Hakurei Barrier, but so were a ton of other characters.

Eirin is a Lunarian, and if her appearance in relation to her relatives, Yorihime and Toyohime, is any indication, Lunarians may be ageless [Think like Elves. Don't die of age, die of everything else]. Of course, that only holds if Eirin isn't a Hourai Immortal... [She got sick in Inaba but Inaba was also rather independent aside from 'This character must appear' and 'general plot points' when it comes to ZUN influence, so Eirin being sick may not be canon. Inaba is a canon landmine.]

As for Tewi, she's an old youkai, but not 'Thousands of times older than Yukari'. Yukari is at least 1,200. Unless we're saying Tewi is 1,200,000 years old, and lived through the ICE AGE. In fact, the wild rabbit of today didn't exist until 4,000 years ago, making it impossible for Tewi to be older than that, unless she's not a 'Modern' rabbit. [Although that date is European Wild Rabbits]

In fact, I've never seen the source that says Tewi is at least 1,300. As for the 'White Rabbit of Inaba'... I searched it, and it calls the tale the 'White Hare of Inaba', so, yeah, Tewi isn't a hare.

[Sagus]

Tengu didn't overcome the oni, the oni simply left after they got tired of humanity's bs.

Maribel is from the future. she hasn't been born yet in the current Touhou events timeline (we know this since, in her world, there are colonies on the moon, and most natural things are gone); it's already stabilshed the she travels through time in her dreams, as the "note found in the Bamboo Forest centuries in the past" published in PMiSS show.

The "兎" in "因幡の白兎" (Hare of Inaba) can also mean rabbit; remember that the distinction between these animals is mostly in terms of behaviour and genetics, and most people confuse the two anyway. As for evidence of Tewi being that hare, Marisa mentions in her book that Tewi's "Ancient Duper" spellcard is "patterned after her crossing of the sea by fooling the sharks in ancient times", which is what the hare did in the story (and got its clothes ripped off as a result), although the translation I read said they were crocodiles, not sharks. Also, Tewi's article in PMiSS notes that "her presence had already been confirmed at the time the Gensokyo Chronicle was first compiled", which makes her one of the oldest living youkai in Gensokyo.

Lunarians are ageless, because of the purity of the Moon; in fact, the only thing that doesn't allow the creatures here on Earth to be ageless like them is our lack of purity.

[Tiamat]

This theory needs a little modification near the end, since we know, with the new cds, that Maribel's powers are now strong enough to transport her and Renko to other worlds, so the trigger that turned her in to Yukari can't be that.

Yea, the base of the theory is sound, but more specifics are known now (like how it's a lot more gradual than I thought it'd be, and how Maribel reached a period where she could take Renko with her. It should be noted, however, that Maribel doesn't fully transport Renko with her. Both Maribel and Renko note that to Maribel, the worlds are reality while to Renko, it's more like a dream).

Eirin isn't a youkai, though, and Tewi's age is only vaguely implied to be really big.

But yeah, as far as we know, Yukari isn't particularly old among the "top tier" youkai in Gensokyo.

but who knows how far back in time Maribel ended up before turning into Yukari

maybe she even witnessed the birth of the oceans  :getdown:

Yea, we know the earliest record of "the youkai that seems to be Yukari" in the past, but that's just the earliest record. It's possible she was around long before then.

Eirin's a lunarian, who generally don't age. Even youkai are stated to age, I believe (I forget where) but Lunarians generally don't due to lacking impurities (though they do have a teeeeny bit of impurity so maybe they age a liiiittle).

Tewi lives a long time because she maintained her good health!  ...if this seems like it's a silly Touhou-esque no-common-sense hand-wave reason, that's probably because it is one. *shrug*

Meiling, if she was actually a Dragon, would probobly be stronger than she lets on. Personally I don't like that wagon *too* much, other than 'Hong' being like 'Long', which is Chinese for 'Dragon'.

Besides the dragon thing, Meiling is also known for having a rainbow theme, which is what the dragon was known for. I personally think it's mostly just symbollic but am open to the dragon possibility, if in part because I find it odd that the dragon hasn't been sighted for over a thousand years...

Yukari-Maribel is oozeing potential. I think it's unlikely Maribel IS Yukari, as they both exist at once, and at the very least, HM shows Yukari awake during the day, meaning Maribel would be asleep during the day. I think a relationship exists, but they are not one and the same.

Unless timey-wimey shenanigans. Always possible with Gaphax I guess. However, we also know Yukari's been alive for quite a while. My personal guess is Maribel is related to Yukari, but is not Yukari herself. We know Human-Youkai hybrids can exist, look at Rinnosuke.

The thing about Maribel's relatives is we KNOW the gist of her family line (well, at least, we know what she knows, I admit).  Maribel specifically says that her ancestors have sought to be spirited away to another world and always had an interest in the occult. That she describes that as their goal implies that they never actually achieved that goal yet. Which means that, for Maribel to be a descendent of Yukari, Maribel's family history must have never found out about Yukari (and Maribel is... well, basically repeating or attempting to repeat what Yukari already did, which is kinda... I dunno, lame if you ask me). We also know that Maribel's family line goes waaaaaaay back, since she describes it as having existed since ancient times (or... something like that. I don't remember the exact wording). Which means that she has grandparents, great grandparents, great great grandparents, etc, all the way back to ancient times. Yukari, meanwhile, has been alive for over a thousand years and lived through many many generations. Therefore, unless Maribel's family history is one big fat lie, it's impossible for Maribel to be directly descended from Yukari because there isn't any room for grandparents throughout the ages since ancient times if it was Yukari that Maribel descended from.

Really, when it comes to deducing how Maribel is Yukari, Maribel being related to Yukari as a direct descendant is one of the few things we can 100% FACTually dismiss (well, assuming Maribel's family history is a fact and isn't a lie). There's simply no way for her to be directly related to Yukari while coming from a line of people that have been interested in the occult since ancient times.

The alternative is that Yukari is a descendant of Maribel, which requires timey-wimey shenanigans, anyways. I certainly can't rule out the possibility, but that seems to be adding an unnecessary step (Maribel going back in time with her border hax powers is one thing, but going back in time with her border hax powers and then having a kid or family line that inherited it and would eventually lead to Yukari is... well, another). Though I suppose that's just a matter of opinion on what's too convuluted and isn't. However, it seems to be at odd with the symbolism of Lafcadio Hearn (which ZUN confirmed symbolizes Yukari and Maribel's relationship). Lafcadio Hearn became Koizumi Yakumo and a well-respected "expert" of sorts on Japanese youkai, and Yukari is referred to as an expert on youkai in SoPM (and implied to be one in the author's comments in Memorizable Gensokyo, complete with author saying "*grin*" as if to imply that was meant to be a clue to something), but I'm unaware of any of his kids moving on to become known for works or knowledge on Japanese youkai. I could be wrong. Finding information on Lafcadio's kids is... difficult. They weren't nearly as famous for sure far as I can tell. At all.

I suppose another alternative is that Maribel isn't directly descended from Yukari, but instead is like, a distant thousandth+ cousin a hundred times removed or something like that. Which, again, while I can't deny the impossibility of such a thing, fits the whole Lafcadio Hearn symbolism (again confirmed by ZUN to have something to do with the relationship) even less.

Maribel doesn't really fit a half-youkai either. One of the things about Rinnosuke is he doesn't age (much). Maribel seems to be aging normally so far (or at least, to have AGED normally so far). If she or her relatives didn't age normally, someone probably would have noticed or brought it up by now (and Maribel does have relatives. She says to Renko, "I don't even have any relatives in Japan!", not "I don't even have any relatives!", implying she has relatives SOMEWHERE, but not in Japan). Rinnosuke also doesn't need to eat much, and is not attacked by youkai, presumably due to his half youkai status. Maribel meanwhile is almost as hungry as Yuyuko in her stories and is attacked by youkai all the time.

In fact, I've never seen the source that says Tewi is at least 1,300. As for the 'White Rabbit of Inaba'... I searched it, and it calls the tale the 'White Hare of Inaba', so, yeah, Tewi isn't a hare.

If I recall correctly, Tewi's comments in SSiB shows she knew Daikosuke (spelling could be wrong) personally. Which implies she was at least around when he was. Which was when the white hare was around.

[Sagus]

Maybe Maribel is Yukari's reincarnation. That'd require Yukari's death somewhere along the line, but since we don't really know how far into the future Maribel and Renko's stories take place, it's possible that she'd die long after all other human characters die.

[Tiamat]

Maybe Maribel is Yukari's reincarnation. That'd require Yukari's death somewhere along the line, but since we don't really know how far into the future Maribel and Renko's stories take place, it's possible that she'd die long after all other human characters die.

I can't deny this possibility either. However, I er... don't really see how that has anything to do with the symbolism of the Lafcadio Hearn Yakumo name thing.

Truthfully, since that's like, one of the few, if only, things where we have complete confirmation of an aspect of the relationship, any relationship between Maribel and Yukari really needs to start with the question, "How does this relate to Lafcadio Hearn?"

[commandercool]

Yukari-Maribel is oozeing potential. I think it's unlikely Maribel IS Yukari, as they both exist at once, and at the very least, HM shows Yukari awake during the day, meaning Maribel would be asleep during the day. I think a relationship exists, but they are not one and the same.

Unless timey-wimey shenanigans. Always possible with Gaphax I guess. However, we also know Yukari's been alive for quite a while. My personal guess is Maribel is related to Yukari, but is not Yukari herself. We know Human-Youkai hybrids can exist, look at Rinnosuke.

Maybe Maribel is Yukari's reincarnation. That'd require Yukari's death somewhere along the line, but since we don't really know how far into the future Maribel and Renko's stories take place, it's possible that she'd die long after all other human characters die.

My best guess is that Maribel and Yukari are related, but not in the bloodline sense. Maybe Gensokyo is in an autistic child's snowglobe, that child is Maribel, and she invented Yukari as an author self-insertion character. :V

Oh yeah, and I forgot that I have a theory that hasn't been covered yet. I've forgotten almost all of PMiSS so maybe there's something in there that outright refutes this, but my theory is that Yukari creates Yuyuko's servants (Youki and Youmu that we know of) by tampering with the Konpaku family's children while they're still in the womb. She manipulates their border of life and death to create beings that can comfortably live in the netherworld but who can freely travel to the world of the living on errands, possibly with the added bonus that their freakiness will make them want to isolate themselves, and therefore be more inclined to be willing to hang out with Yuyuko instead of living normal lives. That's why we've never seen any other examples of the things that Youmu and Youki are, and as far as we know it isn't fully hereditary because it seems to have skipped a generation. Yukari passed over Youki's child or children because he was still fit to serve Yuyuko, but altered Youmu because he was getting old enough that he may need a replacement soon.

I don't have a ton to back it up aside from the fact that Yukari and Yuyuko are pals, it's awfully convenient that Yuyuko was able to find beings that are willing to be her servants and who also happen to have perfect physical qualities to do that, and their nature could be interpreted as the manipulation of some kind of border (because what can't?). Again, for all I know there's some huge detail just hanging out in open canon that completes derails this, but it was a thought that I had and it seems to make sense from what I know.